The first place to start is by taking the boat out of the water, cleaning and assessing the condition of the bottom. If there are no apparent blisters, then you need to decide which type of paint you want to use. You will also have to ask the former owner what kind of paint is on the boat, and then decide if you want to use the same. If not then you need to find out which paints are compatable with the old paint.
Most sailboaters use a self-polishing or ablative paint...but I prefer a hard paint. I don''t race, and I leave my boat in the water for a couple of years before pulling to repaint. I use Pettit Trinidad. I put on 3 coats on the hull and 2 extras on the water line. Might seem excessive...but the paint job lasts and lasts, and lasts.
If you are near a BoatUS store...go in and get with one of their people...they can help you with your questions. They also have Don Casey''s do it yourself tip pages free of charge.