Never used a Napa paint but any other auto paint I have used it is very specific mix ratio that is temp and humidity dependent. Get the plastic cups with the gradations for various mix ratios already on the side. Add the three ingredients in the one cup. Mix and run through a strainer into a good gun. A good gun, compressor with sufficient air capacity to run a gun, water and oil trap, air control at the gun and at the compressor, clean mix, proper mix with right temp reducer and all that is left is technique. Provided prep work is adequate and your in a dust / bug free spray area. Simple right? It can go very smooth and easy or it can go horribly wrong. Practice.
Forgot to mention that most auto paints contain cyanates that you do not want to inhale nor contact any body parts. No skin and no eyes..cyanates like moisture in eyes. So you would also need a supplied air system that covers the eyes and respiration as well as full body coverage.