I made a map for him to mod in the most effective order and gave him prices to look for so he doesnt get ripped off. Its easy to waste a ton of money on modding a car, why not be as eficient as possible? I wish I knew about forums when I first started...

As for the catback thing, a catback exhaust bolts on after the cat, but doesnt replace it. The stock cat is the most restrictive part of your exhaust, so its a good idea to replace it with a high flow cat.