Z axis setup for plasma - have I done it correct ?

I'd be remiss if I didn't point out that at the end of the day the plasmac component doesn't care about the G54 Z work offset. You can literally zero the Z axis wherever you'd like and it will work exactly the same. This because the component uses eoffsets and everything that it does with regard to Z movements is relative.

So long as your Max and Min limits are set correctly, and the axis homes the way you'd like, you should never have issue.

The number that is probably more important is your "probe height". Which will likely need to change based upon torch stick out, material height, etc. This is where the transition from setup speed to probe speed happens. So if you put thicker material on the table, or you have the torch lower than usual in the holder, you may have to change the probe height so it doesn't rapid into the workpiece.