I was thinking we would keep the base doctrines, worldviews and beliefs from any religion that we adopt, and then make a lot of stuff up ourselves. Note also that the religions often are less specific than in Paradox's games - there are of course exceptions, like the fact that they included scientology - but 'shamanism', for instance, is a rather vague term.
Also, we should decide on a civilization. I'm in a hurry and can't find a list of all of them, but if someone can find it, please post it, and start discussing and voting. Everyone gets one vote each, obviously. The choice of civilization from the beginning will only affect the overall feel, but not form of government or language or anything like that. The civs aren't at all as specialized from the beginning in C2C as in Civ5, for instance. Thus, the impact of the decision isn't significant, but we still need to decide.
EDIT: also, the amount of turns depends on the chosen game speed. I don't know which one we should pick though. 'snail' seems to be mentioned often on their forums though.