Tim,
Some thoughts from someone with a few B-ports in his past.
Degrease with something like kero, mineral spirits or simple green. I've powerwashed a few in the past without issues. Be sure to blow them dry to prevent surface rust. Don't strip the existing paint, as you will likely fine 1/2 of bondo under the surface, and will be stuck with what to do next. If repainting, just prime and paint. I'm a fan of the rustoleum industrial finishes which are a good tradeoff between cheap and good.
Phase converters are simple using a spare 3 phase motor (i.e. rotary converter). At the same time, this will allow you other 3 phase purchases in the future. Check out
http://www.homemetalshopclub.org/projects/phconv/phconv.html
Forget the static converters is you have a spare motor around. The price difference is virtually nil.
VFD are getting cheaper, 250.00 will get you one of suitable size, and give you 100% more usefullness. Single phase in, 3 phase out. Dealerselectric is a good source, as is ebay.
The ballscrew machine is an EASY conversion to PC control. Check out gecko drives, which are cheap, easy to use, and interface with a PC without issue. EMC is a linux cnc controller package that is free and VERY powerful. Google EMC BDI (Brain dead install) and start looking for an old laptop to run it on. I think you can get away with a 486 machine. To go full CNC your probably looking at under 700 bucks.
Shoot me an email if you have any questions.