yeah you will need a new exhaust system not a stock one the rb20 and 25 manifolds are the same. in most cases.
injectors, bigger fuel pump ,managment, afm etc etc.
it depends on what you want do you want a 12 second car if so then this is the turbo for you.as for boost it will be between 3500 -4000 but very liveable so you can drive in traffic off boost and when you nail it it will fly. don't stress about when boost comes on cause when you hit boost with this turbo 1 second later you will be looking for the next gear
btw you can run this turbo with stock injectors but just lower boost the stock injecotrs are good for 210-220 rwkw that might be enough for you.
just some ideas.
in my book this is one of the best suited turbo's for an rb25 and should keep you happy. but you need to ask yourself it that kind of power is what you want!
meggala