Is this going to be considered a "Family/Work Safe" site? If so I'd suggest some forum rules regulating language and pictures and what will happen if someone violates policy. At least have someone put a "NWS" or "NSFW" in the thread title.
Chat feature? Are you going to have that on here?
Signature file size setting 500x100 pixels or 2.0kb, I'd figure the avatar setting it 80x80 or 19.5kb the signature file size would be a little bigger in case someone uploads an image as a sig
Lastly. We keeping you busy?