When painting a vehicle, it is up to personal preference how many components like door handles, trim, and molding you want to remove. Just keep in mind that the more you take off and the better you tape with a good-quality masking tape, the more professional-looking job you will attain. Complete mixing directions for PCL's 190 Pro Etch and Polyprimer are available from the manufacturer. If you use the 190 Pro Etch, it must be followed up with the Polyprimer within 1 hour. Mix exactly according to the products' instructions. The Polyprimer sets up very quickly, so much so in fact that I ended up throwing my spray gun away when I was done. My best advice would be to mix a small amount of Polyprimer at a time. I have to thank Harbor Freight for the economical equipment - I'm sure glad it wasn't a $175 spray gun I threw in the trash. When spraying on the primer, use a steady side-to-side or up-and-down motion. Stop at the end of each stroke, and then move on to spray the next location, slightly overlapping the last stroke.