Don't know if you should be listening to the above as he is only 14 and doesn't even own a Skyline let alone a GTR... :lol:
But as others have said, you have a good idea about the mods/power you are after. Exhaust, FMIC and a K&N air filter would be my first few mods to help the car perform alot better than standard.
BTW Welcome to SAU, you'll enjoy it here.
Nath