If your going to use it a lot I would lay it out on paper a few times to get it right. Maybe put a door on the side wall in a permanent frame and a squirrel cage blower in the wall. That way all you would need to do is set up the walls. The booth I now is in a building that is heated and cooled. My door has a full length filter, I buy a roll of AC filter stuff, and the squirrel cage pulls the heated or cooled air from the building into the room, that way in the winter I have no source of combustion in the booth but I get the room nice and warm and in the summer the humidity is reduced because I pull the conditioned air.
If I were going to do it in the garage I would do the same thing, set a door that will always be in place, as well as the air lines, dryer and exhaust system in place also mount a bunch of lights, I have 6 8' long 2 bulb florescent lights and it is not enough or it is the wrong king of light? Last paint what ever walls that will stay in place and the roof and even the floor if possible in a very light color. Then all you would need to do was hang the plastic. You would have a good entry door and ventilation system in place.