1 yes 2 Only if you already have a boat and live near the water. 3 No
But I would suggest using something more like a dead weight testerinstead of air. That is using a piston to pressurize the paint pot or whatever. The reason is stored energy. Lots of energy with compressed air. Very little stored energy using a piston like a master brake cylinder to pressurize the tank. Also if you have a leak you might be able to realize it sooner.
But I would suggest using something more like a dead weight tester