One you hit it with adhesion promotor you should hit everything with a full coat whether it be a sealer or the first color over all of it. Most adhesion promotors have a time window. Mask out the next section doing edges with fine line tape, scotch bright gently and hit it with the second color and so on. The quality of tape can make or break something like this so get some good tape, 3m yellow or green and 3m vinyl blue fine line. Cheap tape can bleed, doesn't release nice, sticks hard, and can pull off underlying paint especially if left on for a few days.
