I painted the topsides of our Capri25 with Interlux Brightside, over three coats of primer, wetsand till I was blue in the face, then sanded more. Everything is in the prep work using black lacquer spray spots and sand with 600 wet, you can see all the low spots, also use a long board this will insure you do not sand more in one area creating low spots in the finish. For the paint I used Interlux products, I used a HVLP gun with a 100 gal. Tank. Several filters and all of the gear to protect myself. A 25 ft boat took me 1 month using weekends, so 8, 8 to 12 hr days.
I would use a two part paint, spare no cost on the materials, and take your time. If the boat is gelcoat spend the time to buff and wax, our boat was painted before so I didn't have the option, but nothing will replace the gelcoat finish..... Nothing.