The main problem with scanning negs is enlarged grain, if you are shooting 120 it won't be too much of a problem compared to 35mm though. Scanning them as a slide seems to help with this a little.
I have had good results from scanned slide film (provia 100f) and then converting to b&w using the carr b&w conversion action I got off the net (the channel mixer never gave me results I liked). Slide film seems to scan much much better than neg, it's a shame since slide has less lattiude than neg film.
As for scanning b&w film, from my experiance despite what people tell you, just forget it. The tonality is horrible and the grain is huge and only gets more ugly the more work you do on the image. My next try will be acros dev'ed in a pyro developer to try and keep the grain under control, but I think it's a lost cause. Some peaple claim to do this successfully though so you could try it.