Hi Steve.
Great post-retirement project and I wish I had your engineering background. I'm very happy to contribute anything I've learned but just to warn you that I'm new to this game so my knowledge is pretty limited.

Re Clive's self-build comment (hello Clive) - I was toying with the idea of building a machine but from what I've read, a steel frame is preferred for reasons of strength/ rigidity/ weight/ cost, and I don't have welding skills or the tools to accurately cut chunky bits of steel box section. Is using aluminium a viable alternative or would that be starting out on the wrong foot? I'd ultimately be aiming to use my CNC for wood only, but although I'm only a simple carpenter, I am fairly exacting so if the design and execution of a self-build machine didn't give me decent reproducible accuracy, I'd be a bit gutted. The cost-effectiveness of a self build does appeal though!
Chris