Rule number one! Take your time even a cheap garage paint job can look decent but 75% of a great paint job is in the prep work this is also the part that takes the most time. If you dont have a clue how to work a gun and lay paint talk to someone who does. And about mixing them paint some paint brands are diffrent ratios pick up a few mixing cups to help you with this part. Also I like to use all the same brand if im laying down a ppg base coat I want to use there brand of clear.Yes some guys mix and match But some are not compatable together. I could go on and on But do your research and have a Idea of what your doing before you even start the prep work and way before touching a paint gun.