It all depends on how far you want to go with it. Unfortunately the short block isnt that strong, probably on par with a wrx, very high compression 9.5:1 i think so it can be a lot more sensitive to boost tweaks and knock, a load of lads on uklegacy.com, go getting it remapped, get it close to or around 300-320bhp and then pop, engine gone.
The biggest restriction on them in standard form is the downpipe and the intercooler endtanks can be known to split the end tanks when the boost gets increased.
I had mine running at 335bhp with a vf36 setup. I believe its running around 360-370 now with the current owner since its being mapped properly and thats with a TD05-20G in it process west TMIC and rebuilt forged block.
properly mapped vf36/37 would be a good option or i think there is even bolt on options now to look at, as changing to any sti fitment turbo requires new headers and up pipe and down-pipe and intercooler etc
So if i was to do it all again. i would start out with forged rods and pistons and all that stuff to strengthen the engine, then the skys the limit really.
Is yours a manual or an Auto? Do a six speed manual conversion while your at it