Oh boy! I just love red Z's! (that's why I own one!)
First things to do. Get the brakes fixed! No fun in driving a car you can't stop. I'm presumming that there is air in the lines. Check/rebuild the rear brake cylinders. This is one of the first places that air gets into the lines. The seals usually blow out when they sit for too long. Rebuild kits are pretty cheap, but if you have to buy new cylinders, make sure you get the correct ones. They are are left/right specific.
I'd get the suspension up to speed next. You have a new bushings set, new shocks, new springs, you now will have a new suspension, all thanks to the previous owner. Money-wise, the price is right! Those pieces you have will make this car handle like a true race car! You won't be disappointed.
I wouldn't use the R200 diff. unless you plan to put some serious horsepower in front of it. The extra weight really isn't worth it. The R180's will handle the power from a stock L28 turbo just fine.
Next, I'd focus on sealing the body up. Buy a weatherstrip kit from MSA or Victoria British. Price should be less than $200 and both companies sell the same kit. You might get catch one of them with a sale, but it's hit-n-miss. The only items that won't be in the kit will be the tail light gaskets. You'll need to but those separately. Make sure you get them. Also get a new shift boot (inner). Replacing all the seals will pretty much stop the exhaust fumes from getting into the car. The only other place left that will introduce a gas-like smell, will be the vapor lines running through the body to the gas tank. You can either replace these or do away with them entirely. There are threads discussing both options here. Just do a search.
At this point, you should have not spent more than $1000 (even assuming you have to completely overhaul the entire brake system {new M/C, new cylinders, new calipers, new brake booster, etc.}). So now you should have a great stopping, great handling, non-smelling car that's a blast to drive!
On to minor engine problems. The ticking could just be the valves needing to be adjusted. Or the oiling spray bar for the cam could be clogged up. Pull the valve cover off, adjust the valves to spec (that's where the factory service manual comes in handy) and pull the spray bar off and clean it out real good. Your cam will thank you. I tune up on the engine is also a good idea. Plugs, wires, points, cap and rotor, shouldn't be more than $100 tops.
As for the rest of the car, you can drive the car without much of the interior in place. That you'll have to slowly piece together unless you buy a parts car with a complete interior. But at least you'll be able to drive a car that will be safe and reliable.
Good luck and congrats on your beautiful red Z car! Now you just need to show us some pictures...