Sorry no one got to this earlier, I think everyone is on vacation or retired. This is the link for the campaign page on FSMODs: http://www.freespacemods.net/download.php?list.40
I post that one because it's the only page I know of where the downloads are all still active.
For singleplayer, Fortune Hunters is a good start as it parallels the events of the show very nicely for an epic 34 (?) missions. After that there's Drums of War, which chronologically picks up where FH leaves off (about Season 5 of the show). Technically, the Earth-Minbari War Demo and Raider Wars precede both of those in the timeline, but I think those come packaged with the Core release?
The TBP multiplayer thread has been dead for years, but there was at least one thread just a week or two ago that shows people still play in their own groups. FUBAR should really field this question, but I'm pretty sure co-op is still viable.