With those pellets, I would say maybe 2-3 per meal, with 2 meals a day. What percentage protein do they have? With bettas, it's important to make sure that the food has a high percentage of protein, around 40%. In addition, the first ingredient should be some type of fish, not meal. Make sure to check to see if your betta is getting good nutrition.
As for the fin, without pictures, I can't say for sure. If he's swimming around and acting fine, I wouldn't worry about it. If you do post pictures, I'm sure someone can help you.