Haven't you had massive problems out of your lsvtec? Make sure all issues are fixed before you even attempt a turbo.

250whp is fine on a stock ls piston, and you should make that easy with the proper turbo kit.

You never mentioned a turbo size so "xx" boost is irrelevant. 10psi on a gt42r is different than a gt25r.

If I were you i would run a t3 size, prob a t3 super 60, t28, etc. Stay away from t3/t4 turbos too laggy for what you want.

DO NOT cheap out on your bov and wastegate. Buy a name brand bov (used or new ) and get a tial wastegate. You don't want eBay no name bov or wastegate

eBay intercooler is fine.

You'll need at least 450cc injectors (dsm or rc)

TUNE!