Stage 1 K03 (GTI) with RTech map will give ~250bhp/300lbft and go well. The little K03 spools quicker than the K04.
Things to look out for on all the 2.0L TFSI cars K03 and K04:
Diverter Valve (DV), these can split leaking boost, straight forward job £35 part - most performance related issues are down to this.
Rusting wheel arches, foam behind the liner gets water saturated and rubs aginst the arch and rusts from within.
Cam Follower, these can wear on high milers and tuned cars, straight forward job and £30 part
PCV (Positive Crank case ventilation), can leak and need replacing, very easy job £35 part
FSH is ideal, especially cam belt/pump