HI,
I weld and have a small Miller MIG. I also volunteer at the USCG shop doing metal fab. The difference between little welders at their max and a 250 amp machine is great. It is hard to go back.
I suggest you invest a bit in yourself first. Find a junior college with a welding program and do a semester or two. They may have a special program to train users doing just what you want to do with a small machine.
Then, decide how into welding you want to go. Used professional machines are available. Check in with your local Miller sales shop for demos and returns.
Good luck, Roy