manufacturer has its own primer that is chemically compatible with the finish coat. Some primers are cross compatible with other manufacturers paints but the manufacturers are not going to tell you which. Go with the manufacturers recommendation.
I would stick with paints designed to hold up in the marine environment
stores generally do not sell these paints.
The most expensive paint you will ever buy is the paint that starts peeling off in a year or two because the surface was not prepared properly or it was the wrong paint for the job.
Although more expensive, I would get a marine
grade paint. For one part paints, go with Petit or Interlux