It's worth noting that emergent communities like this devolve into fascism pretty quickly (as more forums, reddit, & fb groups have proven) so you might want to think about this / bring in someone who is an expert on community management.
Having policies in advance means people will just go elsewhere. Trying to add such policies later, when you have existing users, will be much harder. You're likely to want to draw that line somewhere; better to draw it in advance.
(I've dealt with user-generated content before; please feel free to reach out privately if you'd like to talk about it further.)