McMaster has 1-7/8 ball knobs as well. Check with Reid Tool, Carr-Lane, and Misumi and you may find something closer to 1-1/2".
52100 is probably a bit more corrosion resistant than mild steel, but not much. If you handle a nice clean bearing then set it aside for a few days, chances are it'll have rusty fingerprints on it when you return.I'd be more inclined to call austenitic SS "ordinary" than martensitic. I'll bet you come in daily contact with more austenitic than martensitic SS.
I doubt many folks who've worked with 304/316 SS would rate its machinability as good. I used to be in the marine hardware business so have worked a lot with 304/316 and had large rigid machines to do the work. It's nothing to be frightened of, and there's stuff that's much worse, but easy to machine? Uh-uh. 303 is much easier.
Ned Simmons