Yeah, old geezers like me (I am not going to include you but you may be) used gas welding because there was nothing else. I learned to weld at 13 years old with acetylene by welding beer cans together end-to-end. After about welding 10 of them together my Dad would take them and strike them against the ground. If they broke he would tell me to do it again. I remember I was all grins when he finally struck them against the ground and they would not break. It was a real bear learning to weld something as thin as a beer can without burning it up.
When I bought my MIG welder it came with a roll of flux core wire. I hooked it up and started welding with it. I went about two inches, took the roll of flux core off the welder and threw it in the trash and went to buy a argon tank.
Personally, I like to use .023 wire. I can always turn the wire speed up if needed. .030 wasn't so bad on the older cars but the newer ones have such thin sheet metal it is hard to keep it from burning through. I have no problem filling in a burn hole. I can fill in a 1" hole easily without plating it. I have always had a tendency to burn hot but I move faster to compensate. While in the Air Force I had to certify on aluminum, inconnel, titanium, stainless, mild steel and two others. I had to weld samples that were .030 thick. I learned to move along. One bit of hesitation and there was a hole, and of course, a failure on the test. I had to certify in MIG, TIG, stick and gas. I also certified with low hydrogen on structural steel. I used to be pretty fair, but I am slowing down these days. I was an Aircraft Machinist but I was also required to be certified in welding. It was part of fabricating parts. It was also handy if I had my head up my rear and cut a part down too far, I could weld it up and machine it back down again.