Just a quick comment on Mach single pulse/rev indexing & threading. If your plans include threading steel of any useful sizes, start planning to modify your spindle drive to have a *VERY* stable speed & lots of grunt at the lower end. Your shunt wound motor & modern regen drive may be a lot better than my PM motor/KB SCR drive but I'm having troubles getting consistent results...and this is after building a 4:1 reduction belt drive system for my 3/4 hp Baldor motor. That 3000 rpm speed you mentioned is great for small work in aluminum but pretty much guarantees it'll be far too wimpy at the low end.

Your Z-axis stepper drive's speed & acceleration have a big impact on threading success as well. The faster/stronger it is, the better success it'll have tracking fluctuations in the spindle speed. That's the other flaw in mine, the Z motor isn't powerful or fast enough.

Not trying to throw a stinky wet blanket on your project, just add some info for you to think about early-on. Mine was built up by scraping the bottom of the barrel for cheap parts & pieces and it does a great job for a lot of things; threading just ain't one of 'em.