I honestly would just let the coat be for a while. See how he does, and how his coat turns out. I would not bathe him very often either, though hosing off after a hard workout it fine. Prior to when I got my mare, she spent at least 6 months getting the bare minimum in feed, and absolutely no grooming what so ever, and yet she had an amazing coat. Very soft and shiny, and good color, though she is a gray, so her coat does go through some fugly periods. I still hardly ever bathe her, and only when she's really dirty, and I make sure that I use a very nice gentle shampoo. I've found that some of the color shampoos do a nice job of bringing out the color better. I would just see how he does before adding more stuff to his diet just to help with his coat. He should get a nice coat just from eating good food, and getting groomed regularly. He's very cute, and I'm excited for you.