Serious Upgrades To Do?

[Daboss]

Ok here is the scenario about to spend a few thousand dollars to upgrade my 95 r33 gtst and was wondering what all can i do to get about 400-500 horsepower out of it. Current mods shielded pod filter ,3"turbo back exhaust minus the cat , fmic, ebc set to 10 psi lo and 12 psi hi, stock turbo, stage 3 clutch, 255lph fuel pump and 800cc injectors. Now these are the mods I have in mind bigger turbo, apexi power fc if i can find one,greddy or same caliber intake manifold,80mm afm, 80mm throttle body. What figures should i expect with these mods. also I wanted to know if there was anyway for me to stay internally wastegated as i dont want to change my front/dump pipe set up as it is a direct bolt on to the stock turbo I have. Does anyone have any suggestions as to which turbo I can purchase that will produce the numbers I want that is a direct bolt on and internally wastegated like the stock turbo or do I have to go external and change my front/dump pipe. Sorry I dont have any current figures for u as I live in the bahamas and don't have a dyno to go to get figures or even tuned properly. Just strictly add mods and figure out the tuning for yourself. Attached is a pic of my front/dump pipe. Or is there a way for me to keep this pipe with an externally gated setup?