New build with recycled parts on a ridiculous budget 120cm*60cm work area

[Clive S]

I wonder if my Nema's are underpowered

The Y axis has 2 matched nema 23's 1.8nm, the X axis (Gantry) is unknown nema 23 as I recovered it but is identical size and weight to the 1.8nm's so I assume it is a 1.8nm and the Z axis is a 1.2nm stubby that one is an Italian stepper motor.

In my opinion nema 23's for a router need to be 3.1nm 8 wire, wired in parallel config running at about 4A with AM882 drives at 68V this is a tried and tested solution for many.

In your case I think you are going to slave an axis so you have to think about homing IF using two motors on one axis, so if looking at motion controllers make sure that, that is possible (not all do) Linuxcnc now finally can do this even with a simple bob (as long as you use master 2.8 branch) as it will now home to two axis and be able to offset one to sort out any squaring of the gantry. (this is not an advert for Lcnc as there are plenty of controllers that can do this)
Mach3 can do this as well.