Advice from someone who's learnt a few lessons the hard way and is home sick from work today with heaps of spare time for a long post;
Save up the cash, not the parts. Parts are becoming cheaper and cheaper. It wouldnt be very smart to buy pistons now ($1200 for CP's) for the sake of saying you've got them if you dont build the car for another year (when they'll be less than $1200) For example when i was thinking along the same lines as you CP's were $1500 for the set inc rings, but when i bought a set they were $1200, so i saved 300 by waiting, which paid for all the bearings
To put it simply, here's a list of parts i would buy before the motor comes out;
-Turbos (stock ones on mine were good to 262rwkw, but pretty fkd when pulled off. Go for a few drives in friends GTR's to suss out turbos, if you like the twins just get some 2860r-5's)
-Rods (Eagle, Carillo, PAR, Pauter, Tomei, JUN, HKS, SPOOL are all popular. Get Eagles, they're cheap and work fine)
-Oil pump (N1, JUN, Tomei, Nismo, Dry sump. N1 is popular, so is JUN)
-Manifolds (dont really need them, but if money's not an issue....HKS, Mines, Tomei)
-Dumps (HKS, Tomei, Mines, JustJap. Nows a great time to go for these as the motor will be out soon)
-Valve springs (Heaps of brands, popular choice is Tomei type A and B's)
-Tomei oil restrictor, only one version, under $30 delivered
-Sump baffles, again Tomei are most popular here
-Cam gears (adjustable, HKS make pretty ones)
-Water pump, N1
Leave the rest for once the motor is out, the above list should feed your craving to shop for a while, and by the time you've bought it all, you'll know what most GTR owners mean when they say its not cheap to build one