Any way you want to go is up to you. I have done the spray can paint job on vehicles before, but they dont last. By the time you buy enough cans, you can buy a half gallon of auto paint and have a better finish. I recently painted my race car with an air paint gun and a gallon of paint. This was a full color change, engine compartment, trunk, door jambs and all. Still have over a quart left. If you just want to color the outside, you could use a half gallon would be enough. It wont cost any more than cans. This was my first real paint job, it turned out alright. I will say that the painting was way easier this way as well, and your finger wont go numb.
As far as weight goes, most of the weight of a gallon of paint is the can and the solvents in the paint, when dry, it wont add but maybe 2 pounds at the most. I too dig the old school look, but not the rat rod look. :yawinkle: