Have you looked at a ready made cnc mini lathe, I have a few denford starturn lathes and a couple of Boxford slant beds that i am converting to mach3.

The Starturns are much more sturdy than a standard mini lathe and have been hardly used, and the Boxfords are amazingly sturdy being slant beds. This would save you a lot of work and give you very good accuracy off the shelf.