You cannot play PSO: BB offline. Previous versions were extremely easily hacked due to memory being saved on a memory card, which allowed you offline play.
To remedy the hacking problem, all information is stored on the servers, which requires you to be online to access the information, meaning no offline.
And yes, you'll have to pay the monthly fee.
The servers are going down soon, so I suggest if you have a Gamecube or an Xbox, to pick up a copy of Episode 1 & 2. The xbox version requires the use of a gamer tag, but I've heard you can use inactive gamer tags. So you can try to get a friend's game tag or whatever to use.
Agreed. You can't play BB offline at all, and Sega isn't accepting new memberships for it right now(servers are supposed to go offline at the end of next month, I think). Schthack is free, and won't be closing down any time in the near future.
If you don't remember something, it never happened. If you aren't remembered, you never existed.