Paint Quantity Question

I've been painting cars for 40 years. For what you are planning to do, I'd get 2 gallons. If you are an expert painter and have a really good gun with a high transfer rate, you could get by with less. However, you plan to cut and buff. Plus, if you have about a quart of the SAME paint you painted the car with left over, that could come in VERY handy. I always try to have about a quart left. I think 3 gallons will be way too much for your plans, but 2 gallons will be plenty.