Hello Speedhound,
It looks like a nice machine .
And it will take a serious effort to make it run .
But nothing that a few hours in your workshop cant fix
Is it correct to assume you have changed the axis to ballscrews (there are zero backlash preloaded ballscrews).
If so which kind of bearings you use on the end (the rigid side).
You will need bearings that get rid of the radial and axial play.
you can do that whit one bearing ore a combination of more then one.
On the opposite side they need to be supported whit a needle bearing ore a ball bearing .
In a way they can compensate expansion and shrinkage of the ballscrew.
For the motor it will depend on how fast you want to go whit the feeds.
They have told me for a mill like yours you need about 8 NM on the screw
So if you have 3NM motor it need a reduction of 3 to accomplish your goal.
Enjoy your build.
Kind regards,
Andre.

Experience is the sum of stupidities you have done.