Find a plasma cutter
Read the manual
I had planned to buy the compressor for a kitchen remodel first.
I didn't say buy it, I said find it.
Figure out the one you want, probably based on thickness and duty cycle
How thick of a material do you want, and how hard do you want to work it.
Download the manual and read it.
Some tiny plasma cutters even have a little compressor built in
1/2" is actually pretty thick
http://www.thermal-dynamics.com/
https://www.hypertherm.com/en-US/
Are pro quality machines
Hypertherm is made in USA, company owned by employees.
They are also priced as pro quality tools.
Lincoln seems ok for consumer-prosumer plasma
They are great about putting info on line.
If you plan to use the compressor for other things,
read the specs on SCFM of those tools and make sure you go bigger than the tool.
Horsepower and tank size are meaningless, manufacturers fiddle with the HP ratings. Tanks are cheap compared to pump size and actual motor size.
