waaaaay over doing it
500whp would be probably 600 at the crank. At 2500lbs or so (with necessary driveline upgrades) you'd be looking at a power to weight ratio of a little over 4. Think about that for a second. 10lbs/hp is a decent sports car. 8lbs/hp is pretty quick. And you'd be at 4.
You would also need some decent chassis reinforcement - definitely more than just subframe connectors and strut bars. Add in driveline upgrades, you'd have to do just about the entire thing front to back. Stub axles, CVs, diff output shafts. All of that won't be in any way cheap. And of course your trans will need to be up to the task. I don't know if the stock driveshaft will be an issue.
Now consider that you will need brakes to stop the car, and an appropriate amount of tire to put the power down. This could mean cutting the fenders for flares, but 275s can be stuffed under stock fenders with some effort. With all that in mind, consider that a major strength of the Z is its light weight, and that you would be adding a lot of weight to the car, between rear end upgrades, larger wheels and tires, a larger trans, the heavier RB with turbo, and intercooler, piping, etc.
IMO the Z is not worth turning into a high HP monster. There is so much that needs upgrading, and I think there is a risk of ruining what makes the car great. It should go without saying, that if you still want to go this route, you are free to do so, but you might find the finished product to be more enjoyable if you instead concentrate on maintaining the Z's low weight, while also giving it a much more manageable power level (lets say 300hp). Much less focus will be needed on tire and driveline/chassis upgrades, which will keep weight down (allowing that 300hp to be more effective in propelling the car) and also saving money.
If you want something with serious power, I think there are better platforms to start with. Cars that have strong drivelines from the factory, and a chassis that can handle the power without significant reinforcement, if any. Of course, these cars will mostly be newer.