Highflow turbo, ecu, injectors, afm, clutch, fuel pump.
$4k adventure if you want 240kw or 300kw, need all the same parts. Or you are just stuck with the stock turbo if you don't want to replace stuff.
When people say get a highflow thats what htey mean, rebuild stock turbo with bigger spec wheels. Hypergear, gcg, lots of places do it. Once again you need all the parts listed above if you go a bigger turbo though.