Franois, the little tuning items I see you post about are items you need to deal with AFTER adding more power in a conventional manner, but only if you need to.
Your car will run better with the fewer little tweaks you have to do. There is no contradiction on this Forum that I'm aware of regarding the IAT or Thermostat. 180 thermostats are for 99% of the cars here. 160'* are for the track queens that are heavily modified, and tweaked to work with it. IAT contradiction may be a misunderstanding on your part. There is a difference in how that sensors input is used between OBD1 and OBD2.
In OBD2, there is a MAP sensor as well as an IAT that are used to calculate timing advance. This is why on a stock OBD2 PCM, the IAT trick won't benefit you.
In OBD1 (like yours), the MAP sensor is ONLY for your boost gauge and isn't a calculated part of the timing equation. You CAN trick your timing to advance in this manner, but you will be asking for trouble with your current setup. Your car at this point isn't ready for more timing without great risk.
If you have about 500 to spend, I'd concentrate on the basics for now. Get a better intake (FWI), keep the 2.5" pulley for now, and remove your exhaust manifolds. Repair all the cracks (remove all the heatshields), and stitch-weld the outside of each runner to the flanges, then port out the OEM welds. Between the intake and exhaust manfolds, you'll gain 15-25hp and it will set you up nicely for more power. It might also be a good time to port-match your LIM to your cylinder head ports (PORT-match, not Gasket-match).
Many of the little 'tuning items' are just that. For tuning. Not for power. If you want to make real power, you have to flow better all through the engine.
In the meantime, start saving up for a transmission. You'll need about 3-4 thousand for it before long. As soon as you start modding a car of that age, it'll be coming. And you can regain much lost performance with a good rebuild, and even more with a good shift kit.