Is there going to be support for moderation transparency? Moderation bias seems to be an issue in these kinds of "closed" discussion platforms.
Do you intend to have admin/moderator actions visible in some way to the users? If posts are edited or removed (by users or mods) does that get indicated in any way?
Different approaches to these issues can significantly affect how a community grows, and I'm always very interested to hear how new sites choose to approach the problem.