Thanks JazzCNC

It's not very clear on the design, but the intent is to use a belt with pulleys, 1:1 timing. (Very similar to JoeHaris' design) - as I've read, it helps with resonance and gives me the ability to do 1:2, or 2:1, or other rations if I allow a variable positioning of the Nema (which is the intent)

I looked at Profiled Linear rails - just seems to cost a tad more... although, would be easier to fit to the Aluminium profile... Will see what pennies I can get out the couch :)

Thanks for the 3.1Nm vs 4Nm motor advise - I think that's one tick I can put next to - "Buy Nema 23, 3.1Nm motors" :D

Once I have all the input and design tweaks, I'll know what length ball screws to get - So recommendation so far is RM1610 (with the end an extra 15mm for the pully) [This should give a resolution of 0.05mm (at full step) and 0.00625mm at 1/8 step - that actually pretty decent! ]

As for Slaved motors, should I go with 3 Nema's (One belt connecting both Y Axis to one Nema ?) - this will save on buying one driver and Nema, but worth it ?