Um, with this new religion, are there any rules or commandments? Any special celebrations?

Well, we worship the Cullens obviously, and that includes Bella. The only celebrations that I'm certain of are Edward and Bellas birthday. You believe that the Cullens are real and that Stephanie is the (or one of the) best authors ever. You believe that if you are good on Earth you will spend eternal life with the Cullens, and if you are not then you will be sent to James' cave. I think that's decided por the Volturi. Umm...OH! And you should read at least a page of a Twilight book a dia :D