for about 400bhp you are probably looking at the following.
larger injectors,
Remap ecu.
forged pistons, (and all the cost of reboring, new bearings)
NA oil squirters,
Uprated turbos (even with stock size you will need upraded internals)
turbo boost controller.
Larger intercoolers,
Larger radiator.
Exhaust,
Induction kit.
Lightened crank pulley.
Clutch
When I rebuilt my engine more money was spent on what I would call support mods than actual power increase mods. Ie. new wiring loom, water sensors, o2 sensors, PCV hoses, larger radiator, larger intercoolers, clutch, metal gaskets, new lifters. Basically stuff that would give me no performance gain, but needed to be uprated or in top condition to work with more power.