steel tube build concept - 1500y,1000x,250z

[JAZZCNC]

My suggestion is forget Plasma the cost is too high and by that I don't mean cost in money but strength/performance/hassle.
The high Z axis will cripple this machine for anything but light duty cutting. Plasma is messy, smelly and expensive to do right. Your electronics will need to be geared towards it other wise you'll have potential for major hassles from EMF and is area where taking short cuts or cost cutting will bite you quickly.
Plasma and Routers just don't play well together and best kept separate. Also Plasma machine is basic in strength requirements and building required so easy enough to build a low cost stand alone frame to do the Job. Just make the Electronics interchangable with Din plugs and have Plasma profile Setup in software.

Having a High Z for 4th axis is also costly in performance/accurecy terms but often desired thou seldom used in practise so why cripple the machine for something you'll maybe use 5% of the time.?
This doesn't mean you can't have 4th capabiltys just design the machine in such a way that the 4th axis is off the machine. Either at the side or on then end then design the gantry or frame so you can reach it.!

No harder to build really just different but with no compromise in strength or accurecy as router.