you would not need a license unless you put a sign advertising what you sell.
you should get permits, because if you get fines, its going to cost you lots more than paying a permit. with a permit you can open your own location near the beach. In order to do what you want, you need a boat and good fishing material, because there is lots of competition for fisher men in PR.
also the deep waters is were the good fish is at, otherwise you will be fishing seaweed.
