At the end depends from the budget , i believe.

I am in the same situation like you, though now i am deep in building a router so the plasma build is postponed a bit.


Now my personal conclusions on the subject, may change with time, but the main is simplicity:

1. Dedicated or not?
Definitely dedicated plasma machine.

2.Which linear?
Depends on the design. For such small plasma table/and for bigger, when dedicated/ my choice is wide Hiwin low profile MGW 15 or similar

Why:
- most are stainless steel rails
- low profile
-1 rail and 2 bearings on gantry and z
-available dust seals
-wide profile rail will straighten the gantry

3. Ball screw, or belt?
With ball screw prices i cant see a reason not to be implemented, but my choice definitely will be belt, given that everything is done light/ gantry and z/.
Belts can be placed more strategically than screws and are quite more resistant to the fine dust that the cutter will produce, cheaper and cheaper to change.
Especially if you don't intend to make a water table.

Choosing wisely the belt will make the machine extremely fast and precise. Additionally is simple to build, can be clocked on the long axis and so on.

4. My main concern will be implementing THC torch height control. A must.

Hope that helps.