Ballscrews - pulleys - timing belts

I want to retrofit an old semi big lathe 1.6m distance between centers.
So i got 2 servos 1.8kw 3000rpm 6Nm.
I must choose between pulleys/timing belts or shaft coupler (ballscrew-motor)
(I have already ordered X axis ballscrew+ballnut 1605 L700mm + single ballnut)

Because i have not experience for this construction
i want to ask what will be better for Z/X axis ballscrew diameter/pitch single or double nut and what will be better ballscrew-motor coupler or transmision with timming belts and pulleys.
The lathe now has leadscrew diameter 30mm pitch 4TPI (~6.35mm) and has prismatic ways for Z axis and dovetail ways for X axis.
Any suggestions that will help me iam looking for a good combination?