This thread is really abuzz now Sean, and I, like the majority of forummers here are rather dumbfounded by your intention to downsize your wheels and brakes after reading your initial post and stating that "...a lot of research, now i know the power and history of the GTR" If you have researched enough you will find that NOBODY has downsized regardless of the make other than for circuit/motorsports purpose. Don't hold your breath trying to find a 285/85 R16 tyre with wheels to go with it...
Be it a Nissan OR Lambo, you will find that owners DO NOT downsize and replace smaller brake system in return of achieving cheaper maintenance. It just simply goes beyond our comprehension that the thought even crossed your mind and I am certain your brother will disown you if he found out. This brings about some discrepancy to your story told where you claim that you bought it from your brother that has migrated, but in your 2nd post you said that you are going to take care of it on his behalf???
But if your plight is sincere, then my advice to you is "if you have to ask the price, then most likely you can't afford it"
Last but not least, this is a Nissan forum whether you like it or not... so don't knock the brand and the enthusiastic owners that reside in this virtual community.