Help choosing hardware items

Hard to answer as there are many possibilities, from using a parallel port with cheap drives like TB6600 for stepper or BTSnnnn arduino drives for servo, but i woukl go for a Mesa 7i95 for steppers or 7i97 for servo. There are also cheaper Mesa boards for stepper systems starting with 5i25 or 6i25 or 7i92.

Plasma cutting and milling do not mix together:
-plasma cutting requires fast cornering for cutting thin sheets, meaning low weight gantry and Z axis, small motors, belt driven or rack and pinion with significant reduction, high acceleration, no external forces acting on machine parts.
-milling is mostly the opposite, heavy everything, big motors, ballscrews or rack and pinion with much higher reduction, lots of forces on all moving parts, etc.
Also, 2-3KW motors are used in 15 ton machines, 0.75 to 1KW are more than enough for that size of router, 0.25-0.5KW are more than enough for plasma.
As a side note, it is much easier to build a plasma machine using stepper motors as plasma source produces huge amounts of interference, meaning if servos are used a lot of attention in regards to grounding and shielding.