Just a note to help anyone asking this kind of question, which right now includes me:
First, decide if you want to do a real, frame-off restoration where you disassemble the entire car and completely attend to any rust on the frame or body before repainting it and reassembling the car (i.e. serious investment of time and money, best done on a car that is already very solid), or whether you just want to clean up and update a running car.
Assuming you want a runner, a Z or ZX is actually a fairly mechanically robust car with fairly good parts availability compared to many less common old sports cars. The biggest problem on these cars is rust, and the best thing you can do for that is to wait before buying until you find one that looks very clean both walking around it and especially up on a lift. Particularly check the frame rails, crossmembers, floors, under and behind all wheel wells, under the doors, under the battery tray, etc.
Once you have a car in hand, get under it and arrest any rust you find as much as possible by cleaning it up and putting on rust inhibitors like por-15. Cleaning up the cosmetics of the body work is more tempting but probably actually less important in the long run. Next, identify any mechanical or technical problem the car has and start to identify how pressing it is and how to solve it, particularly anything that isn't right with the engine or transmission. Do reliability repairs under the hood-- plugs, wires, replace any brittle hoses, fix any leaking seals, replace long-wear items like the alternator, belts, radiator, brake components etc. unless they seem to have been done in the last ten years (history and receipts are good if you have them). This is all basic stuff you would do with any old car.
Next, and focusing now on the example of the ZX, it's common to update the whole suspension: all new bushings, struts, better sway bars if you want them, maybe also do a normal overhaul of the brakes and steering as well. It's easier to make a ZX handle very well than to make it accelerate a lot faster, and all of this is shade tree mechanic stuff with easily-sourced parts. If cosmetics are important to you and you've taken care of the body, then you can redo the seats, carpets, fix or cover the dash if necessary, fix any little faults in the cabin, replace the hatch struts.
Once all this is sorted, you probably need tires and your exhaust is getting close to dying. Clean up the wheels while you're at it, get a bigger exhaust, and maybe improve the air intake too for a little power bump. A couple of other parts will need to go, maybe the fuel tank or lines, or the clutch, or who knows what. Finally, there are two big concerns: replacing parts with what you wish the car already had (wrong steering option? wrong transmission? seats, wheels, turbo, etc.) and, eventually, rebuilding the engine, probably with a few power tweaks. These are big projects, you'd have to search for them separately. Once all this is done, the car is effectively restored-- so you'd better go back in and check on all that hidden rust again.
