To answer your questions, I work almost exclusively with acrylics. Most of the colors are from Archive-X and a couple are Model Master.
I do airbrush the main colors and add the damage topically with fine brushes. I just play with the thinning ratio to find a good mix that levels out well without leaving brush strokes.
I've used a few different clear coats over the years. Testors dull coat was great but it was discontinued. Vallejo makes good quality clear coats too. I've tried Krylon but it doesn't spray very smoothly.