I'm thinking of re-making my old BBS as well (TrionBBS - available on Aminet, I even got the keyfile again from the author).
I'm not planning to set up a dial-up connection though, so maybe I'll have to make some piece of software to fake a dial-up via some sort of ip-connection.
As far as your questions go:
1 Yes, but not too regular
2 Retro-feeling, and for fun
3 Probably not (sorry)
4 Not much, but I'm no speed freak at all actually
5 As many as possible :-)