You can buy the rear diffuser for the mk7.5 gti and get any gti exhaust fitted on. You will need a smaller downpipe adapter since the 1.4t has a smaller one than the 2.0t
Old thread, but I am running a gts race chip on mine with the k&n filter and love it. I run 91 octane all the time and only use the higher maps with booster. This car has been super fun for the 5k I've had it. Very peppy, and I can get up to 40 combined mpg. It's not as fast as a stock gti but...