Referencing this thread: http://www.clubwrx.net/forums/cockpi...ggestions.html
So, your first mods were a catback and a BOV. Your next planned mods are a bigger turbo and a MBC?
Your questions are: "What else do I need to replace w/ the turbo?" And "How much can I turn up the boost?"
My friend, you need to do A LOT of research on how to safely modify your turbo Subaru motor.