Bike looks good. Although no one mentioned it before, the key to a GREAT paint job is the primer...if it sticks and bites, the rest of the paint job will last. I owned a custom paint shop for 7 years. I painted everything from motorcycles to street rods to bicycles, mtn and road. I learned from trial and error, mostly...luckily, there weren't too many errors in the way of durability. I mostly used DuPont automotive products.

Honestly, I wouldn't recommend using an airbrush to spray a frame. They are good for details and graphics, but overall spraying is very difficult if you want a premium finish. The wasted paint you see in the air is really just part of the game. Ask anyone in the body shop or paint shop and they will tell you the same, ESP. when painting round tubing.

Your paint job should hold up just fine. Enamel is very strong, when applied in the correct amount. Too thin and it will flake, too thick and it will chip&peel. Acyrlic Enamel is just another formulation of enamel, so they are similar, but compatability usually depends on the brand. By the way, don't mix brands.