Agreed with Iamhe77. If your stepping up from a R33 GT-R, looking at a R34, the M35 is a bit of an odd ball!
As far as modification goes, pretty much anything that you can strap (enginewise) to a Infinity G35x, V35 sedan, or Z33 will either fit, or require a little bit of modification to suit. There are twin turbo kits out of the states for about 7k atm, suit stock motor, but if you want GT-R numbers your up for a rebuild with forged internals. Frankly, I don't know how much power the PNM35 AWD system will take, because I don't think anyone has tried it! You'd have to look at big hp G35x's in the States for a lead. The Yanks have done heaps more for the VQ35de than the Japs, thats because of the G35 coupe and sedan. Parts from there are inexpensive, and sometimes an outright bargain at the current exchange rate (almost 1:1). You can make over 1000hp, if you have the pockets to deal with it (much like anything i guess!)
Yes the auto is a downer, but you have no choice. No AWD manual available.
Ultimately, if your after a drivers car nothing will compare to a GT-R. I suggest coming down to sydney and driving a PNM35/PM35/NM35 or even anything with the V35 platform VQ35de and you will soon get the picture. If you have s**t to haul/ family/dog and are after something different to a commonwhore or whatever, the M35 is awesome.