Given where you are coming from and where you are going, then I would have thought that threaded rod for a short-term, cheap, solution would be fine. Can it handle high speeds? No. Can it handle heavy or 5-days-a-week commercial-type use? No. Will it wear out nuts fairly quickly? Probably - but see below. Will it work and give you something to play with, as well as do something useful, while working on Mark 2? Yes. Use stainless rather than BZP as it's much smoother, but if it's any reassurance, the M10 leadscrews on my JGRO router together with the Delrin nuts have been in use, intermittently, for the last 3 years and have done many useful jobs in that time. They are far from being the weakest part of the design. And I've never needed to adjust the anti-backlash nuts in that time.

It's always possible that this machine will encourage you to be even more ambitious for the Mark 2!