That's a more radical departure from the usual imageboard model, but it might be interesting. I'd still need a meta-thread to discuss what could be played next, and I was thinking of making some more boards, too…
Maybe they could all be like this, and have a set theme that changes regularly, and then have a /meta/ board with automatically created threads each time one of them changes, and a voting system of sorts.
And if we're going all the way, I might use a read-only archive for the older threads. I could also add a feature that lets you choose whether to archive a post or not when you post it, though that could easily be abused.
As for the multiplayer server, I could schedule a day/time every week when people are free and can play.
I really don't know what to do for advertising. Do you have any suggestions? I'm still counting on word of mouth.