As a first time fiero owner too (now 2.5 years in) I can offer some suggestions for your car.
Go through everything that moves. New shocks, brakes, bushings, Check the radiator, new hoses. Things have deteriorated over time.
KYB shocks & struts work well. ROck Aut oseems to have good prices on brake rebuild kits from Centric, about $4.00 per wheel.
The steering rack may be an issue and you can't find new ones.
If you are after fuel economy then look elsewhere than a 2.5 Duke with the 3-speed auto. It is not an efficient engine and the 3-speed auto gives a cruise at 70 MPH of almost 4,000 RPM. Engines of that era are early fuel injected designs that are antiques compared to anything modern. If you do a swap a 2L inline 4 with a 4 or 5 speed auto would work wonders for fuel economy and probably be much quicker. My 2.8L V6 is lucky to get 20MPG at 70MPH. I doubt that the Duke engine, only 0.3L smaller, would be much better.
My car was a 2M4 1988 also. Looks the same as yours only red and now has a GT nose. The prior owner did a swap for a 2.8 V6 and then ran out of time due to job, wive, divorce so it sat for 12 years. I'm now in the midst of a V6 swap from a 2018 Impala, LFX 3.6, 6T70 auto. Most everything else has been fixed and updated since I bought it. I'm expecting a cruise MPG of 30+ with the final ratio being 2.77 with 5th & 6th gears being overdrives. My biggest issues were the steering rack was crap, replaced with an earlier Impala power unit using a MR2 Spyder Power Steering pump. Vacuum leaks that never seemed to go away. Took a long time to find all of them. Ignition problems since the old disty was crap, the modules don't last due the stupid engineering that put it in the disty which runs 150F+ when the engine is hot. Finally a blocked Cat Converter.
Best of luck, keep reading the Forums since there are lots of guys out there who have found ways of making the cars last and run much better.
[This message has been edited by MikesFirstFiero (edited 04-22-2021).]