We choose Subaru for the first one because david is dedicated the United's ideology, and also has a hand in Subys. He's gonna head up the new chapter.
As for the forums, what I'm thinking is they'd all be the exact same forum, only the tech topics will be hidden based on which forum you're currently viewing. For example if you go to the forums via the ub.c domain, it'll show e36, e46 etc. If you go to the forums via the us.c domain, it'll hide the e36 and such forums, and show the wrx, sti, etc forums. The lounge and all the rest of the subforums will be shown no matter what. Then I'll add another little block for the number of posts in the UnitedBimmer chapter's forums (e36, e46, etc), and the number of posts in the UnitedSubaru chapter's forums. Since it's just a modification of the forums themselves, the memberbase and active users online will be the same on both sites.