To answer one question, 8, 9 and 10-speed hubs are the same width (130 mm OLD) and so are all of the cassettes so choose whatever you want. The amount you will have spread the frame will be identical for all of them.

I presume that by 1994 Bianchi had gone to English threaded bottom brackets but I'm not certain of this. If it's a Shimano UN (i.e. sealed cartridge type) you can't rebuild it. If the bearings are bad or it's the wrong width for what ever crank you choose, you have to replace it.