I'm not sure about the edge of the fins, but if you're uncertain just make sure to give him lots of clean water. If he has rot, or torn fins, or chewed his fins, that will help it clear up and prevent rot. Since you just got him it might clear up with regular water changes, feel free to add in aquarium salt, that pat recommended, and yes, a good diet is important!
Live foods are considered the best, but frozen bloodworms will be devoured. A good pellet is also beneficial. I like to feed my boy 2 pellets in the morning, and 2-3 frozen (not freeze dried) blood worms in the evening.