I used a propane infared heater in my old detached garage
I don't even go in the garage at my apartment its barley big enough for the car
if your going to fiinish the walls I would put some kind of plywood over the insulation instead of drywall its more durable and gives you tons of mounting options for shelves and cabinets later and you can still paint it
I have a 26 gallon 1.7hp oilless husky at my house it runs most air tools ok but it can't keep up with a sander or a grinder .Its really loud.
my old compressor I left at my parents was a 1940's vintage westinghouse with a 60 gallon tank and a 10hp 220v motor running a single stage pump this unit is very quiet
whatever kind of compressor you get try to stay away from the oil free kind they are loud as hell
I enjoyed shooting it, big enough to use during deer season, I didn't mind the recoil much, and they make holsters so you don't have to hold it in your hand all the time
that said its out of my price range for now