for the nailers, you will need a compressor that can give you a minimum of 100 PSI pressure. for other tools, it is the volume of air that determines size. I have a 20 gallon 2 hp that is ok for everything except painting and sand blasting. with these, you fork for 1-2 minutes and wait 3-4 minutes for the compressor to catch up on the air supply.

a good source of a large, used air compressors is the classified newspaper ads and also you may find a good deal at a pawn shop as the pawn shops do not like BIG items taking up room on the floor.