Much has been said already, but to reiterate.
1) Do NOT cheap on the welder! One
can do decent welds with a cheap sealley. But the cheap welders are not particularly forgiving for a novice. The more expensive welders will have better quality wire drives and more stable electrics. They will also tend to go lower on the amps. You do not need a 160 amp welder to do car bodywork!. You do however need a 25 amp one! I have one of
these and am very pleased with it. (You can order it with a spot/plug weld timer which is a useful addition)
2) Use argosheild (Or similar) Again, one can do reasonable welds with CO2, but argoshield is more forgiving. One can get "Proper" bottles from places like
albee-weld which for occasional use is a lot cheaper than BOC.
3) Preparation is everything. MIG relies on completing a circuit via the arc. The slightest particle of rust or paint will interrupt this, as will any gassing from nearby paint etc boiling off, so you need to clean the metal of all old paint near the work area.
4) Practice on scrap metal first!
5) Dont forget the welding gloves etc. If working overhead wear ear muffs! (Welding spatter in your lughole is a tad uncomfortable and welding spatter comes equipped with Lughole targeting AI!
)
6) Make sure you have the means to put out any fires that might start! A turned on hose pipe with a trigger nozzle is pretty good! and be vary careful if the car has ever been waxoyled!
7) Make sure you have plenty of spare nozzles/gas cups. While you are learning you will get through these