I'd start with something far simpler (and less pricey to maintain) for your first bout of learning. A Z32 is cool as heck, but plan on a LOT more needing replacement than just tires and a head gasket.
At that point, you may as well go through the engine completely, and if the HG went south, I'd suspect cooling system issues... You're also going to want to do belts, hoses, water pump, thermostat, most likely injectors, brakes, fuel pump, all fluids, and THEN pray the t-tops don't leak (most all do, unless seals are new).... I'll stop there, but I'm not done.
I also see rust (which means you're gonna snap some bolts), missing vacuum hoses, and a lot of janky ricer-boy crap that would make me walk away fast.
$4k is high for a non-runner. Seller is on crack. If it was that simple, he'd fix it himself.