OK - Go to a paint supplier and simply buy acrylic lacquer with a compatible thinner - General Purpose thinner should do. I'd say no more than 1ltr of base color will easily do the headbox and the cabinet. Mix 60 thinner and 40 paint (you can do 50/50 for primer). Set the gun to around 35 PSI and practice on an old piece of timber. Let the paint almost dry and play around with the gun (airflow and paint mix) until you are happy. Before you know it, you will get the hang of it. EXPECT to make mistakes. This is how you learn the gun, compressor and paint. You are effectively bypassing Trade School by learning on the job. soon you will love it !

Do all coats of topcoat in the same session - don't paint one coat, then sand, then another coat and sand.. wait 10 minutes inbetween coats. That's my preference, but it might not be right in theory.

Paint in a well ventilated area. Wear a breathing mask AND goggles. Why eye protection ? Because last year my touch up gun blew black paint and thinner straight into my eye and it stung like hell ! I lost half a day at the Eye and Ear Hospital - so cover all the safety issues BEFORE doing anything.