I would say the possiblities are limited only by your budget. Here are some photo's of my bigger projects with the miller 135. The shed is 24x33 build in 2 sections so it's portable all welded with 110v miller hooked to a generator. The back hoe bucket was done with the little mig & a stick welder as the quick attachment plates are 3/8" thick and the mig would not weld that. I use 25/75 mix most of the time. The trailer was a rebuild that I put new fenders on and painted. I do have a larger mig that I have been looking @ but I the guys @ IL-MO got me to try a plasma & I purchased it first, as I have a stick & 110v mig. I got a miller plasma that will run on 110v or 220v. Being able to run on 110v is a real plus as you can plug them anywhere.
I was looking at a used Miller 135 for my first welder, but it sold very quickly. Saw the new Miller that runs on 110 or 220 and that looks like it would be a good one to start with. It runs just under $1000. That plasma cutter you have would be a great companion to it. Whats is the thickest material you have cut with it? I think it is rated up to 3/8.