If you are going to use the airbrush more for detailing, then I would go with a dual action. You can control both the air, and the paint with one control. A little tricky at first. Practice, practice practice. As for tank size, I can't answer. How much painting are you planning to do at a time? Again, if you are detailing, a 5 gallon would last quite a while. Why not just run off your large compressor? With a regulator of course.