Scoobykid3

I am starting a project and am unsure on what to do so that I can get the best performance from my subaru impreza gc8 1998 track car. It has
fully adjustable hks suspension,
A full roll cage
2 bucket seats
Aluminium bonnet
Carbon fibre spoiler
2 aluminium lower wishbones
An aluminium exhaust... Think its fully decat
Taken out the spare wheel area and going to replace it with an aluminium plate
Taken off the exhaust mainfold heat shields
Taken out the full interior... Including damp proofing
It has a standard ej20 engine and a standard ecu with a standard td04 turbo

I was thinking of replacing the engine with a 2002 wrx ej20 2.0 engine which I have and the full wiring loom so I can remap it.
But I dont know if I should or not also I am unsure if I should use a vf34 turbo or a td05 turbo.
Also I want a k and n air intake but is this the best thing to do?
Im replacing the radiator with an aluminium one and using a front mount intercooler too. What else should I replace to make it the best possible without spending too much money.i am still learning a lot about scoobies and apreciate the help