1) By all means. Abaissé is going to be heavily reorganised as it is. A few of the boards will remain the same; a lot will be renamed and/or regrouped; a couple might not be returning. Among other things there is definitely a separate forum for "Nerdy Fan(girl) Research" but now that you mention it I'm not sure the threads like, say, "Quatre-vingt Treize" will belong in there. So perhaps another fanboard will have to do.
2) Um, this one I might not do, merely because we have both a livejournal community whose posts can/will be locked to members only once I've gotten around to it, and because Marianne claims to be working on a website for us to plan things with. I don't want to make too many public plans, but the livejournal community can easily be locked so that only the people who are members of the community can read the posts -- and therefore comment upon the plans that are made. The Barricade Day planning hasn't been very concerted just yet and that is starting to make me antsy, as here comes November and I haven't bought my theatre tickets yet. Although I need to stop rambling on that before I get off on the wrong tangent...!
3) Do not know that's possible with phpBB. As far as I understand it, I've been on other forums with a chatroom where some of them were just separate services linked to the board, and not necessarily built into the software. Until I can reliably confirm the ability to install a chatroom on phpBB AND verify that it can be so configured as to allow only Abaissé members to post on it, I'm... not going to do it. It's not going to be part of the planning for the move/upgrade, at least.
We could always set up a specialised IRC channel or AIM chat room should anyone be so inclined, however.