Peter ... I think the core team's going to rapidly grow to include quite a few more folks than the TAB team. My concern with weekly IRC chats is just one of trying to herd 8 or 10 folks into a single chat session on a normal basis. Forums nad mailing lists aren't synchronous and that might be a real advantage for a group that size.
But I'm not personally beholden to any particular approach to communication among a core group of folks.