If you're talking about buying those cheap Chinese stepper motor and driver kits on Ebay, don't waste your money. This forum is full of people who did, and then had to buy something else when they didn't work. If you want to retrofit a lathe or milling machine with CNC controls, the best thing would be to find older machines which already are set up for CNC, but which have broken or obsolete controllers. These can often be found quite cheaply - cheaper, actually, than equivalent manual machines. Once you've got that far, then go shopping for an appropriate control system - you may be able to reuse the existing motors, if you can figure out how to drive them. If not, then do some research before investing in a control system - there's a lot to learn about.
Making those timing-belt pulleys in brass from scratch might be more work than it's worth. There's a reason most of these things are die-cast. The brass stock alone will be pretty expensive. You'd need a pretty good-sized lathe to turn them on, before refixturing them on a 4-axis mill to cut the teeth and drill for the set-screws. Then you can broach the keyways with an arbor press and the appropriate tooling. I don't think you'll need to do any knurling, though.