Go Eddy. My GTI had the turbo go into retirement, the new turbo was awesome at stage1 (retch) but then the clutch needed upgrading. Was expensive
I would have gone K04 but your talking exhaust, FMIC, HPFP, injectors, new map, KO4, clutch... labour unless your brave. You would be looking at 320-350bhp then maybe a diff and uprated brakes... depends how far you want to go.
there is also the seat cupra option as stated earlier.
KO3 and KO4 are different power deliveries, depends what your after really.