Depends what power you are chasing. If the car already handles fairly well and your not looking for over ~200kw get a front mount, some form of engine management/ piggy back unit (Emanage ultimate, SAFC - PFC's for RB25's are getting to the $1300+ regions these days if you can find one) and get the car tuned.
If you want more power than that your going to need to start looking at an upgraded turbo, injectors, a Z32 AFM, and clutch. A basic piggy back unit like the SAFC will not allow you to run these modifications correctly.