I started with a rocketchip "1.5" (the real rocketchip, not the scam company advertising online now). That was the highest he would go with a stock turbo. Real nice bump - the way the car should have come from the factory. Once you go farther - it will snowball.
Next is bigger turbo and of course a matching tune. IATs will shoot up and your clutch WILL slip (stock lasted a little while). FMIC to address IATs. Eventually your EGR cooler tubes will fail. Install a better flowing intake manifold to remove the cooler. BRM flows best, "euro" PD150 style second best (anything is better than the BEW manifold). Then you'll find you have no traction with a 1 wheel drive fwd car so better tires and suspension and a limited slip. Stock fuel system will handle 150-180hp-ish (I still have a slight haze of smoke at 24PSI on WOT).
After all that, buy a 3.0 V6 TDI that comes stock with 240hp and 420tq and AWD but still gets upper 30MPG
(then tune it too!!!)