As a suggestion, get it laser cut or water jet cut instead of plasma cut. You will get a cleaner edge and you won't have to grind every edge before welding.
If you do get plasma cut, you MUST grind the edge of every area you will be welding or you will get porosity in the weld and it will be weaker and look like s***.
The laser or water cut give nice square edges for better fit-up and no pre-grinding required.
When you design your plates, make them corner to corner fit, not flat, tee, or butt joints. You will get better welds and a better looking finished part. If you don't know what I mean, let me know.
Someone will tell you it's "just like a laser. It's high definition plasma.".
No, it ain't. Get laser.