Welcome,

First thing to do is start a Build log here. Plasma Build Logs

Doesn't matter if you haven't got design together yet just state your intensions and thoughts just a little bit more than you have here and ask any questions that your not sure about. Folks will drop in and give there opinions sure enough.
I'm not big into plasma but the basic principle is just same has router based machine just you can get away with lighter weight machine and gantry. Other than the Plasma side like torch height control then the electronics are just the same. The main difference is you MUST NOT try cutting corners here has Plasma produces lots of electrical noise which will quickly drive you BONKERS with strange happenings.

Best advise is go trawl some of the other builds for a design, ask loads of questions no matter how dumb you think they may be and Most important DONT BUY ANY electrics until your sure they are correct for your needs.

Good luck.