Hello, we do custom mapping unique to each hardware setup so we don't state must have hardware at each stage. All we say to customer is work out a budget and power range you want then plan from there. The power comes from getting the hardware flowing it's best, the more research and reading you do the more you will gain and "could" end up saving money as the expensive brand name bolts are not always the best for flow/power.
Stage 2 u can get away with just induction kit and downpipe Decat. To get the higher numbers and more area under the curve at stage 2 you would want to go full exhaust, decent induction kit, fmic ect and also budget for a clutch.
Ball is on your court in regards to hardware, but remember with mapping the hardware is always the limiting factor.
Nick