a compressor thats atleast 2.5hp should be fine. if the car has paint on it, use thick sand paper like 120 grade to start with, then use a 400 grade and then a 600 grade, make sure you sand with a block and not just by hand as it leave grooves, make sure to bog any dents and sand flush. wipe down the car with grease and wax remover to get rid of any oils/grease on the surface. spray primer on with a thick nozzle say a 2.1mm and do a couple of thick coats. once primmed give it a quick light sand with a 800 grade sand paper. wipe down with grease and wax again, then start you coats of paint. do the first layer light, then build up with a couple more thick layers, remember to sand with 800 grade in between coats, after the final thick coat do a sand with 2000 grade, give it a buff and you should be fine
no im not a painter by trade but have done a few cars and all have come up nice.
hope this helps you guys