Any welding supply store should be able to rent a bottle to you and you can just get a mini bottle for at home. I've been welding quite a bit with mine and still have half a tank. Use .030 wire for sheet metal applications. Your welding machine manual should have a matrix chart with wire feed speed(amps), and voltage for your wire/metal thickness that you are welding. The best gas for mig is a tri-mix. it is mostly Argon with a little CO2 and believe it or not a little O2. The manufacturer up here in Canada for this gas is Air Liquide and the gas is called Almig. When welding keep your wire stick out to a minimum(more bead control and less amps/heat), weld with a trailing motion( same as writing if you are right handed) left to right for flat welds to prevent burn through( you are depositing weld metal on weld metal rather than heating ahead of your molten puddle and burning through) and down hand for vertical seems. Also, to keep spatter down to a minimum try to keep your nozzle angle perpendicular to your workpiece. Use some scrap to experiment with the angle.
Also for filling gaps try "triggering it", pulling than releasing the trigger every second or so to allow the puddle to solidify in between pulls.
One other thing, if you are going to go with the argon gas mix(the best and not too $$), you may need to change the male fitting that goes into the bottle as it is different than a CO2 fitting. The regulator is the same, its just the end piece that screws into the bottle that you need to change. They are about 5$. A can of anti/spatter spray goes along way with saving your tips and also a quick coat on surrounding components helps with cleanup. I like the spray better than the gel for that reason.
A good starter project for a mig is a cart for it.
Cheers and good luck,