As I have said on this site before being a stain guy I’m not a big fan of paint, however when I do paint, a good primer undercoat helps the paint cure, which seems to make it more accessible to most overcoats. By trial and error, I found a simple artists matt varnish for use with acrylic paint from the arts and crafts store works great on paint or stain it does not matter if its water or oil based. I get a good clean protected surface. Also, with all trial and error testing keeping good notes is a must. You will always have to go back and touch something up, your reference notes makes matching the touch-up easy. I even go so far as to label and keep the good test pieces as a future reference.