If your friends are real
vegetarians they won't eat anything cooked in the same cooker as a piece of meat. I only mention this because I had some VG friends who said "oh I can't eat that" (it was a vegetable) I said "Why not?" they said "because it was cooked alongside meat" as in the same vicinity.
Ughh. So pretentious. Needless to say I never have them over for dinner!
Sorry for the short rant, that stuff just gets on my nerves.
Good luck on your first cook, keep it simple, give yourself plenty of time and don't stress out and you'll have lots o fun!
As for your VG friends, flip em a can o green beans lol