a. It's never been more affordable to own an R34 GT-R than it is now.
b. Anyone can own a gtr, it's really not that hard.
From the experience I've had, they are quite a reliable and rewarding car to own and drive, albeit a bit heavy. Every car has their inherent issues. These cars are no different.
If you can, pull off the rocker cover so at least you can check the general wear and tear. A car that's serviced with regular oil changes should have a very clean head.
Coilpacks are a common problem with most r34's. They'll just die and replace them with Splitfires or equivalent.
Check the bonnet lining. Unless it's been changed in the past, it will give you an idea of how hard of a life the car's gone through.
Check for signs of panel repairs, although it's more than likely these cars have had a bingle or two due to their age. As long as repair was done properly, there shouldn't be a problem. My advice, don't get an MP II or III. They are next to impossible to colour match. The base chromium colour alone costs several hundred bucks per liter. Then you have to add the multitude of tints to get the colour right.
Give it a good launch to check the Attesa is working properly. You can check the torque split on the MFD. A good solid launch will yield almost 50% split. If it gives you a weak reading, you know there's a problem somewhere along the system and it could be costly to rectify.
Don't rely on the kms. Chances are it's wound back. Check for wear and tear on the driver side seat bolsters, gearknob, steering wheel, pedals. That will give you an idea of the real kms travelled, unless it's been changed of course.
The diffusers, especially the front can and will cop a battering when the car is lowered. Hell, even standard height they can cop some serious damage and they cost about $1500 brand new from Nissan.
Underbody rust, another common problem with these cars. Actually all imports really.
I can go on but at least it's a start for you. I'm sure there's plenty of other, more knowledgeable people here that can chime in.