keeping short
you need low compression piston,rods and bearings .
better headgasket.
upgrading head is not compulsory it's optional. turbo build need strong bottom end.
turbo.
headers.
turbo piping including turbo cooling piping.
intercooler and it's piping (not necessary to install a freaking BIG intercooler. size depends upon boost).
wastegate ( turbo got internal wastegate adding another is optional)
blowoff valve
providing more fuel.
and most important a chipped or aftermarket ecu and a person to tune that according to your setup.
i maybe forgetting something.