Definately two drivers with two motors. It's theoretically possible to do it with one ... but don't go there!

Those drivers are not very good at all - only 27 volts. You should get at least 50V, or 75V. That will be more like £200 for the drivers and something for the breakout board ... there's a cheap 5-axis one on eBay.

One breakout board will suffice, unless you run out of inputs later on. You just need as many power supplies as required to get sufficient power to the motors. I used a 500VA, 75V (when rectified) transformer for 4 motors ... it's ok on 5 too.

CY, 4-core cable 1.5mm^2.

Don't worry about the electronics, I'm sure I/we can assist...