if you wanna push it harder, you will need bigger injecors. the tune may be alright, just have less margin for crap fuel etc.
what was your last ride before this? an R34 GTR with 380rwkw would be an absolute weapon, if its a street car, stick with what you got, as your just going to add more lag with gains that probly arent all that great, and you may find that the car is actually *slower* in most typical 'street' situations
if u wanna race it, strip it bare (coz its free) and go run some numbers