ko4 upgrade help please
 

Hello all. hoping for some help. I just got a TT 180 2002. 91,000 miles well maintained car. the heads were rebuilt, along with timing belt, water pump, and tensioner by Audi at 75,000 as part of the Audi sorry we have crappy timing belt campaign. The only modifications that I can tell on the car is a cat back exhaust with dual tips at muffler and a newer "forge DV". Here is my question I understand the car is equipped with the ko3, if I swap it to a ko4 and have the ecu redone by APR install a down pipe and remove the cats, and install a large air flow filter, what else needs to be done to the car. IE; do I need to replace intercooler, injectors, etc. Also what kind of hp gain will this get me, I understand the Ecu upgrade will get me about 209hp. Also the best for the money turbo.
Thanks for any help :D