With the DVDs coming, and the reruns starting over with "The Gathering Part 1" later this month, I suspect that traffic in the B5 forum will increase. The Crusade and Rangers fora are likely to be fairly quiet with only the occassional "what if" story speculation thread. I think that perhaps B5 should retain its own forum, for the series and the telemovies (among which I'd include A Call to Arms, which starred Sheridan, not Gideon, and was really the last B5 adventure, not the first Crusade story) and merge the others (perhaps including "General Discussion" which just confuses people who think it means "off-topic" or "other TV shows" anyway) into a "Spin-offs" or "JMS's other works" forum. The books and comic books could mostly go here as well.
B5, being both the source of the fictional universe and the only show that is both complete and still on the air, will likely have an on-going life. Unless there are books or future TV movies that involve Crusade and/or Rangers I don't think there will be enough traffic to justify maintaining them in separate fora. The thread titles should be enough to keep discussions of the two apart, so I don't think their being "too different" will be much of an issue. People only interested in one or the other will simply read the threads they care about and ignore the rest.
Just my two cents.
Regards,
Joe