If your going to do this, then do it right, you need a mig that is able to cope well with thin steel, yet handle penetration that is required for 1/4 plate, that will cover you for welding things like brackets, exhaust mountings, bolts, lawnmower parts, wrought iron.. you get the picture, I would consider nothing less that a 180amp mig running ideally on Argoshield gas, however, for Argoshield, you would need a BOC account, and for many reason, that is easier said than done! though your mig would work perfectly on the cylinders of Co2 that pubs use to pump beer! do you know a friendly landlord! although the correct guage is needed. I'm still on the same bottle that I liberated over 15 years ago!! disposable bottles are a pain, expensive, and guaranteed to run out at a critical point, Its sods law!
Get yourself on a good night school course, and lots of practise makes perfect
Tom