If you want just a small upgrade over a stage1 om stock hardware, then GT1749VA from AWX/AVF(+ hose from turbo to intercooler hose. It has another sistem to fit the turbo), is your first choice. I suggest you to but also intake manifold+egr + the black pipe +map sensor+ airbox+maf+turbo intake hose if you want the full performance. The intake parts on pd100 are from older engines. If you want to stay on budget, take only the 3bar map sensor, but 051A, because your pipe has big hole, not small like AWX.
Bv43 is the next one, but together with a secondary intercooler on the right side or fmic and most probably your clutch won't hold the extra torque and the entire upgrade is pointless.
Before starting changing parts on the car, make some logs on channels 3, 10, 11 om gear 3 and 4 from 1500 to 4200. Then keep an eye on n75 values on the log from channel 11. If are bad, buy a new one.