to reliably get 300rwkw you will need a rebuild, a bigger turbo is a must (although you did not mention what you have, with 190rwkw i assume its not standard), oil pump will be fine but may need upgrading depending on what you want to do with the car, bigger injectors, i think a z32 afm will do the job, standard gear box will be fine depending on usage.
Try looking in the rb25 dyno section, that will show you what people have to achieve the power you want.
Also what is a 3 stage heavy duty clutch?