In freshwater, the two issues are slime and algae growth and zebra mussels. Epoxy won't resistant either of those.
If you are racing, a popular boat paint is VC-17. It is a thin film high copper content paint. I think Petitt makes a comparable product. Look for SR in the name, SR = slime reduction. VC-17 goes on easily, dries almost immediately and is reasonably economical. On my Sabre 30 I would use about 2 cans maybe a little more or less. The down side to VC-17 is having to remove it. The copper can build up and sanding tends to burnish it, not remove it.
If you are just cruising and day sailing, an ablative paint will work. For the past few years I've been using Blue Water Marine Shelter Island (
https://www.bluewatermarinepaint.com) it is a copper free paint that is reasonably priced and works reasonably well. I have not had any zebra mussels but I have had some slime on the south side of the bottom where sun can get to it. I plan to continue using it for the foreseeable future.
If you take the paint off to the gelcoat, it should be repainted with a barrier coat, like Interlux Interprotect 2000, Blue Water Marine makes a similar product, prior to applying the antifouling paint.
Check with neighbors in your marina to see what is working for them. Also, Jamestown Distributors does a survey every year about bottom paint. Check them out:
https://www.jamestowndistributors.com/userportal/search.do?tag=getting-to-the-bottom-of-paint