Welcome to Nico!
Interesting situation you have here, I'll start by saying that you will need to spend probably $2-3K on maintenance and repairs on a Z that's at that long, and possibly the same doing upgrades to the car to be in the range you spoke of. This costing reflects having the work done (labor), so any work you can do will stretch your budget. Therefore until you assess your needs with the car, I'd go for taking your grandpa's offer and maybe paying him some $ if the Z plays nice (not likely after 10 years sitting) and doesn't need much repairs beyond the 120K maintenance and other things such as the injectors and harness.
There are several good vendors for our car that carry a broad range of parts such as Concept Z Performance and Z-1 Motorsports, and many others that can be googled or are vendors on this site such as Powertrix and Wiring Specialties and Interior Innovations.
Be sure to read the stickies at the top of the Z32 page as it does contain a very broad range of info towards your interests that can be accessed any time- Everything You Need To Know About The Z32 is a must read. Be sure to save the Online Service manual in the stickies, it's a life saver for repairs.
Good Luck, and post her up when you get her going!
