Interesting Ray and sounds fun. For me and tunes and mostly/tending towards Irish.

1. Life would mostly alternate between G and D (or one or two sharps) and most tunes have pretty established "session keys"

2.Tunes (typically 2A 2B) go 2 or 3 times round in sets. Sometimes a set may be agreed beforehand, sometimes a set may be an established one for the session, sometimes its a case of trying to pick up what the next tune is (and deciding if you know it to play) as quickly as one can. A set may usually be 2 or 3 tunes but sometimes people can add other ideas to that as things progress.

3. Percussion can be a touchy subject. I think a good bodhran player can be an asset but...

4. Squeeze boxes very much part of it. And pipes...

5. Yep at best the whole becomes greater than the sum of the parts or something like that..