Really, I'm just bouncing back and forth between excitement that I might finally be taking harp lessons, and not having a clue of what I should be looking for or avoiding. Help, please!

Someone asked me about this earlier in April, so here, have an infodump from the post I made in response on LiveJournal, now that I've noticed this thread, in case any of it helps.
1) There are many different kinds of musical goals..One of the very few online discussions I've gotten into that made me really seriously crabby to the point that I still am was someone insisting that anyone taking music lessons less than twice a week was not at all serious and shouldn't even bother with lessons or music.
If that's your thing, and you want to do that, and you have goals where that makes sense, go for it. (And there's someone on my FL who can speak to this approach.) However, that is *so* not the only way to approach music. I've spent my whole musical career (with regular lessons in one thing or another from ages 5-22) with weekly lessons at best, and often long breaks over the summer (though I did keep practicing). It didn't kill me.
I am not good enough to perform classical music professionally - but that was never my goal. I *am* competent enough to do what I want to do with it, or to get there if I actually practiced more often than I have been. (More than that, even the performance majors at my college generally had weekly lessons, unless they were prepping a recital or something.)
If I were looking for lessons these days (as someone with solid musical skills, but out of practice), I might look for every 2-4 weeks: it'd be a good fit with my available practice time. When you're just starting, you want lessons closer together to avoid picking up bad habits (and this is particularly problematic on harp, and I'll get to that) - but a lesson for every 4-8 practice sessions is probably adequate even then. There are teachers who can accommodate this - and really, if your goal is "Get better, but not stress", you want one of those teachers anyway.
2) Know what you want lessons to do.Do you want to learn the basics of an instrument, so you can work on your own? Different set of needs from learning repetoire, or developing to be able to play in a group, or accompany others, or learning specific advanced techniques on the instrument. Also, know where you're starting from. If you've learned other instruments previously, it goes faster, generally, even if they're not related. If you don't read music, you're going to be learning two things at once, in many ways. This will take more time and energy than just learning the instrument.
(How much is variable: depends how you learn, how your teacher approaches it. I am the wrong person to ask about learning to read music as an adult, because I've read music as long as I can remember, and the method used for me doesn't work well for adults anyway.)
3) Teachers have different kinds of passions.This is particularly true with harp. There's classical/orchestral harp, and there's folk harp. While there's some cross-over between the two, they're not interchangeable, and the *goals* of the two often really aren't interchangeable. (Orchestral harps are a huge investment, for one thing, so people generally only learn them if they're serious about pursuing orchestral playing.)
My harp teacher played orchestral (very well), but she was also really comfortable teaching folk (and did a lot with the Scottish/Highland Games in New Hampshire, actually.) She was also absolutely committed to the idea that people could do different things with the instrument: how she taught me (as a late-high school/early college person for whom it was not my primary instrument) was respectful of my goals and desires. How she taught people for whom it was their major instrument was different. (And, in fact, in a couple of cases, she very specifically handed them off to other teachers after a particular point in their training.)
(Oh: harp teacher was Stephanie Curcio - which I mention because she's also got a line of intro-harp books, arrangements, and other cool stuff.
http://home.comcast.net/~scpron/ )
Anyway, you want a teacher who can teach compatibly with your goals.
4) InstrumentsThere are many folk harps. It is well worth investing the money to get a decent one. (Does not need to be top of the line). Note that the very cheap ones (with a notable exception) tend to hold tuning *very* badly, making the instrument annoying to play, and which will disincline you to play when you only have a few minutes.
The real question with folk harps is number of strings. Anything under about 26 is going to be at least potentially a lapharp. 29 and more are larger, and will require a stand/legs/etc. They're less portable, but you get more bass notes, and can play a wider range of music. Wood choice makes some difference: some woods sound better younger, some age really well.
There are lots of other variants for construction: more Celtic ones have a larger body, rounder shape, etc. I highly recommend trying out harps in person because how it fits your body matters.
My harp is a Stoney End Lorraine model - 29 strings. She's walnut, which I was told takes longer to age, but sounds better (especially in the lower range) when it does. I'd highly recommend Stoney End in general. (They're also mid-range: excellent quality and tone, but not as pricy as some of the other folk harp makers.)
The one I've been lusting over for a while as a "more portable thing to bring with me more places" is a Harpsicle or Sharpsicle: these are made by one of the major harp makers, as an answer to the cheap Pakistani harps out there. They're made in the US, by people paid a living wage, but they're intentionally simple. Someone on my FL has one, and loves it. They're ideal for an inexpensive but still well-made instrument. They're light, and are ideal for walking and playing, etc. (I want one for ritual use, among other things.)
http://harpsicleharps.com/Various broader harp options include wire strung (you need fingernails or picks for these, and they're a specific technique not all harpists do: nylon strung, you typically use the pads of your fingers), cross strung (way cool, but I wouldn't start there) and the issue of sharping levers. (which get their own topic). There's also stuff like electric and jazz harps, which I know far less about.
Oh, yes. String colors. Convention is that all C strings are red, all F strings are blue. This helps you figure out where you are.
One final note on instruments: harp is unlike a bunch of other instruments in that the actual spacing between strings varies a bit between makers and models. Because of this, it can be hard to swap from harp to harp. (Your fingers learn to expect certain kinds of spacings. Plan for transition time.)
5) Sharping leversOrchestral harps have pedals to change keys (you shift the pedal with your foot, and all of the F strings become F sharp. Or whatever. You can actually go two ways: up a half step, or down a half step. This is important when playing with lots of accidentals or key changes, as in orchestral music.)
Folk harps can have sharping levers: they allow you to raise the pitch of that string half a step by flipping the lever. Levers are mounted right at the upper string attachment (the bridge) and you flip them by hand. (Which means taking your left hand off the strings for a moment if you have an accidental in the piece.)
If you want a good range of keys, you don't need all of them - but F, C, and B are the most likely to be really handy. (B lets you do pieces in F, and then shift the lever to B for C, G, or D or their associated minors/modes without retuning. Really, I don't think I've ever used any of the other levers, but I mostly do folk stuff or my own compositions, and I almost always write in G or D or related modes.)
6) Useful accessories:a) You want an electronic tuner. You just do. I've got a good ear (and more to the point, a well-trained one over the course of years), and I still far prefer the tuner. There are many harp strings: it is a pain to do them by ear. There are different varieties. There are harp-specific ones with pickups that you can clip inside the sound box: many common tuners won't pick up the highest edges of the harp range (about the top octave or so) well. I have a regular ($30 or so) tuner, and just do the last octave by ear.
b) Carrying case. Excellent as you will need to move your harp occaisionally. If you intend to carry it around a lot, invest in the heavy duty case. If you just need to move it rarely, the lighter duty one works with some extra padding (blanket, coat, etc.) You usually need to get these based on your harp: the shapes vary between makers somewhat.
c) Music stand: basic cheap metal ones work fine. Fancier ones exist. Something to hold the music, and that adjusts low enough to be comfortable.
d) Something to sit on. It's not entirely comfortable to play a folk harp from a standard chair (though it's certainly manageable - the angle's just slightly weird.) A lower stool is great. Something portable helps when you go other places.
e) A metronome: useful for practice, this lets you start slowly, and build to faster speeds while keeping rhythyms even. I have a little credit card size one with a seemingly never-ending battery. (or maybe that's just a sign of how little I use it. I've had it since high school, though, and it got regular use for a long time.)
f) You may want to invest in a set of replacement strings: up to you. It's handy to have them on hand, and I definitely suggest that if having to wait for them to ship would be a big deal. When I started, you had strings on hand because there was no online ordering, so you had to either get to a store, or get hold of them, or whatever. These days, shipping and ordering are so much more efficient, it's not as big a deal.
There are all sorts of music gadgets. Find what works for you.
7) Speaking of tuning…There's the old harp joke: "How long does it take to tune a harp?" "Dunno: no one's finished yet." Lots of strings = lots of chances for something to go out of tune. I am horribly erratic about playing and tuning mine, but she's held up really well. You do want to consider where the harp will live, and ask about relaxing the tension if you're storing for a long time, have erratic temperature changes, etc. In general, you usually want to keep some tension on (rather than relaxing all the strings like with a guitar) because the soundboard will warp.
Replacing strings and other maintenance.I am not very good at replacing strings: I need to go bug Stoney End about showing me again. (I cannot for the life of me make a knot that doesn't buzz.) Fortunately, it happens rarely.
It is fairly common for a harp to have a quirk - a string that tends to go out of tune, snaps more frequently, etc. (Mine is the G an octave and a half above middle C.) If you keep having problems, it's worth having it looked at (sometimes it's a rough edge where a string rubs or something.) but mostly, this is part of the cost of playing an individual instrument. It's usually not a huge deal.
Beyond that, a little basic dusting, etc. works well. Be careful of wood protectors, oils, etc: they can change the sound of the wood.
9) Music and booksThere's a lot of stuff out there, but it can be hard to track down. I've heard good things about the Sylvia Woods Harp Center (and they have a free catalog):
http://www.harpcenter.com/faqs.php is her FAQ page, with some other cool stuff. Stoney End also has a paper catalog, I believe. Or if you call and talk to places, and tlak about what you want/are playing/etc. they can suggest things.
The Sylvia Woods arrangements are decent, but a little complex for my pleasure-playing amusement. (and as she points out in the FAQ I linked to, you will have trouble with some of her arrangements if you have a 29 string like I do.)
I'm really fond of "The Three Ravens, and Other Ballads, Arranged for Lap Harp" by Suzanne Guldimann (which is a bunch of ballads, with words.) and she's done several other books I want to pick up.
http://www.harpcenter.com/page/SWHC/CTGY/BAuthSGil gets you covers and info. Click on the title of each for a list of songs.
Last time I was at Stoney End (about 18 months ago), they gave me a free back issue of Harplight, and I really liked it. (And intend to subscribe/etc. when cash happens again.) Even cooler, each issue includes a 1-2 page piece for small harp. (And interviews, articles, etc.)
http://www.harplight.comI have plans to do a bunch of arranging and such once the job/school/move thing settles down, because there's a lot of stuff I want to play that I don't expect to find arrangements for. (And hey, the music degree's got to be good for something, right?)
10) Why picking up bad habits on harp is problematic:Harp, more than most instruments, is extremely reliant on what your fingers actually do - because they're the mechanism that directly produces sound. (Rather than wind instruments, or bow, or whatever.) Even more so than guitar, because you're using three fingers + thumb independently of each other, and each finger presents some functional challenges to playing evenly, getting from note to note, etc.
(Three fingers rather than four. Why? Look at your hand. Note that ring finger is longer than pinkie. There are people who use all 5, but not because it gets you extra range - it actually shortens it slightly.)
Anyway, given all of this, how you learn to move your fingers, pluck strings, move hand away after plucking, etc. can make a major difference on sound. There's also a lot of stupid little stuff that if you learn right the first time, later more complex music is a lot easier - and if you don't, you'll either have limits to speed or complexity, or you'll have to completely retrain your body.
(Harp is also a very kinethestically played instrument, in my experience: you feel what you're doing far more than seeing it or even hearing it, and a lot of what you need is best done by settling things into muscle memory - this is how far from my body middle C is on this harp, etc.)
There are also just some weird physiology things. As an example, put your hand flat on a table or the floor. Try picking up each finger in turn. (Lifting it straight up.)
Most people have *real* trouble with their fourth finger. Skilled pianists generally don't, and touch typing doesn't hurt either. For harp, you need all three fingers to move independently with as close to the same range of motion - if you don't have someone giving you feedback, it's particularly easy to cheat that last finger. Also, they can spot other things that may be easier or harder for you, and give you things to work on that help.
Erm. Treatise, yes. Any other stuff you have questions on?