youre going to need a decent manifold (avoid xspower and ssautochrome), a good turbo, t3/t4 .57+ trim and around .63/.63 or bigger.
piping can be obtained eithere from ebay or friendly muffler shops (as well as the down pipe). Get a decent BOV (ebay knock off is fine) and a good wastegate. the B18C is a good platform to start from. if it were me i would replace pistons, rings and rods and keep the head stock.
after that its all about tuning, new injectors (for 300 your can still just use DSM turbo injectors) and keep the P72. Chip it with crome and tune on a dyno. If the tune goes well you can probably make 300 and keep under 10psi (meaning dont have to upgrade the MAP sensor).
Its pretty general...youll be pushing 5k with what i listed. including internals.