Rasboras are beautiful fish and the only reason I would say no is the fact that they have very lovely fins. I am afraid my little Betta pals would find those fins very tempting to nip. It would be a problem that I am afraid we could not help and it may cause you some distress. The Compatibility Charts from Live Aquaria.com lists them as compatible though. You can draw your own conclusion and see when you go to look at them whether to buy them but I do know that they nip at the fins of Platys and so judge by the length comparison to see if you think they would be a problem.
Corys or Otos are good additions; they don't even vaguely resemble a betta and are mostly scavenger/cleaner fish. Apparently you can keep most of the livebearers with them but I'd be careful and be ready to take them back.
Well if we are talking about 1 Betta (2 1/2 inches) and 4 Cories (they average 3 inches) and then you would have room for 3 Otos (1 1/2 inches each) that would leave you 1 inch of fish to go unless you go with Dwarf Cories (2 1/2 inches) and they you could have 4 Otos. How is that?
That sounds like a fine tank to me, and Bruce would not have too big a problem except he would probably chase them for a bit until he gets used to them but he will settle down after a while when he knows you haven't forgotten him. It is an attention thing.