If you are just swirling pedals, you shouldn't need much paint at all. You should be able to do it on a much smaller scale than guitars and need much smaller gear. Only need enough water to make sure that the pedal can be totally submerged and not hit the bottom - width wise, same sort of deal I should think. That said, if you are looking to sell them one day, I wouldn't try to save money on the finish by scrimping on paint...