*a large collection of deities, both general, and local (local streams, mountains, and rivers and such)
*Celts where not pacifists, in fact, they where many noted warriors among them, and when invaded, gave the roman legions a difficult time.
*there is much that we do NOT know, and in some cases, we will have to recreate reasonable (to us) facsimiles that fit into the framework while at the same time work in the sense of pleasing the deity(s) and offering a spiritual path for the practitioners.
In terms of reconstructionism (to which I would like to answer - although I realise the bounds of this group is a little wider than that), recons tend to focus on a Celtic culture specifically. This usually means Irish, Scottish, Gaulish or Brythonic - it depends on the flavour. CR is an umbrella term, therefore, and in many respects, so is the more specific cultural identifier - I would say I'm a Scottish Recon, but I focus specifically on the area I now live in. I always have - where I live now is an added bonus in that respect. In practice, this means I recognise and mostly focus on the Gaelic heritage of the area but also the Brythonic heritage that leaves its mark on the area (I live on the Clyde, so I include *Clota, probably a Brythonic deity. It's complicated...).
I'm not sure I've ever met any CR nor any Celtic Polytheist, of any flavour, who truly believed the Celts - any Celts - were pacifists. The myths and archaeologists are pretty much conclusive on this. Nor do recons claim to be doing things *exactly* as things were done in pre-Christian times. Yes, we look to the sources, to history, to archaeology, to more recent folklore in order to inform our ritual practice...We don't claim it's exact or authentic. Nor do most other Celtic Pagans I've encountered, except those who want to make a fast buck, to be honest. Luckily those are few and far between.