Lots of info can be found using the search button...
Sound is very subjective. Short tails are typically loud. If that's what he's going for then, great. If he wants gains, then a full CBE and test pipes might do better with similar sound. A tune will help get the most HP out of your bolt-ons. Fast Intentions makes a great exhaust - it is generally the go to exhaust around here.
Plasti-dip is very polarizing in this community. I'm not a fan of the look, so I would never recommend it unless one is doing it for protection. Some people use it to accent all sorts of pieces on the car. To each their own, so it's whatever he wants to do. Some people are going to like it, and some people are going to hate it.
Again, there is lots of info on both of these topics. A quick search will net you better results than this thread, I bet
