Alright, I've been working with 1st gens for a few years now, let me share a few words.
First, carburator: PAUL YAW! He modifies the stock carburator and is the best in the business.
http://www.yawpower.com/
Second, exhaust: Can you get away with a high-flow cat? If so, get rid of the stock CRAP. You have 2 precats and a main cat. They're heavy and EXTREMELY restrictive, as is the stock header. Get rid of them if you can. Note: Heat shields hide exhausts very well(wink wink).
www.racingbeat.com
Third, suspension: Wheels and tires are subjective. If you can, get a set of 1983 Special Edition 14" rims. Still light, but 14"(more choises). Honestly, tires are the best suspension mod there is UNLESS your stock suspension is warn out. If you need to, replace the stock springs with Racing Beat and shocks with Tokico blue's or Illumina's(depending on budget).
Fourth, lightweight flywheel and clutch: You'd be AMAZED how fast your car will rev. Guess what? You have an '85 which means you have the lightest rotors Mazda ever made until the RX8. It'll be a bit of a b**** to drive on the street(rev higher, slip clutch more), but its a whole lot more fun to drive.
Fifth, porting: An agressive street port, or even a mild street port, will increase power by a lot...especially with the Yaw carb.
One more thing: What model is the car? If its an S or GS, you'll want to look for a rear-end from a GSL. Limited slip and disc brakes are on those, and make the car a lot better.