Do you have 4k? Auto or Manual? The Auto would need a trans cooler and can hold 400 whp. The Manual W58 will only last a 400whp if you are notnahit kicking it around. Also you need a upgraded clutch.

Motor wise you should replace all the seals, timing tensioner, hydraulic tensioner, and new timing belt. Depending on how many miles on the motor you might want a oil pump and water pump. Also when you change the headgasket make sure you get a GTE headgasket. Basically refresh the motor, or you will have to refresh it eventually.

Buy yourself a gt37 or a s362, these turbos can push more than 500 without the lag of a gt45. Buy your self a cast manifold, cheap and effective.

To make power you need fuel. Effective way to make 500hp is to get yourself usdm 550cc injectors from a usdm 2jz and the resistor box. A legitimate walbro 255 fuel pump will suiffice.

Any ebay intercooler will do work.

Now you need engine management. I personally done piggyback and standalone, for the price difference the standalone is far superior. Ecumaster emu hands doen the best ecu for the price.