Lets eventualy start this CNC - MKI

[JAZZCNC]

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 :)

Dig deep because worth every extra penny.

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

Remember Inductance not all motors are the same even if same Nm rating.

[This should give a resolution of 0.05mm (at full step) and 0.00625mm at 1/8 step - that actually pretty decent! ]

Don't Full step action will be rough and Don't really think of Micro stepping to increase resolution and more to do with having smooth running motors. Buy Digital drives and you'll get lovely smooth motors with less Micro stepping.

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 ?

Yes that's what I would do using 10mm pitch screw with 1.5:1 ratio which increases torque and still gives decent performance. I've used this setup on machines with heavier gantry than yours so know it works ok.