For intakes, I have NEVER seen one installed that didn't throw A/F ratio off, even though they ALL advertise they don't. As much as 25%, usually in the midrange! The amount of knock correction your car does to make up for that sickly lean condition will hurt your performance, and the "need new maf" statement is just bogus. The only reason you would ever need a different maf "housing" is if your maxing out your current maf, (5v), which is usually around 450whp. I currently never recommend anything beyond a drop in filter (except maybe on 08+'s), because it's simply not worth it. For the exhaust, a cat-back is more about sound, I can claim from experience the gains from a cat-back are very small. The downpipe is where you get your gains, lots of extremely hot gas needing to get past that turbo. By the time it gets to your cat back it has cooled so much you could argue that going to what most use (3") is actually too big, because the velocity of gases slow down so much. I would suggest what most the major tuners suggest which is, drop-in filter, 3" downpipe, and tune and call it a day. In the end you will have less money in it, and a much better running car.