First off - this is a learning experience for me, I'm trying to learn about how cars and engines work by modernizing my 1990 Toyota MR2 with a bone-stock 3S-GE in it. I don't know a lot about this stuff and have close to 0 practical experience.
Currently I plan to modify it in two stages, and am looking for advice for the first stage now:
Stage 1: Modernize the engine management
Currently the four cylinder engine is using a mechanical flap to measure intake volume, and a single coil/distributor based timing and ignition system.
My intent is obviously to put in a Speeduino based ECU, upgrade to coil-on-plug with sequential ignition, and remove the old bulky and probably faulty air sensor in favor of a temperature sensor. I'd also like to replace the old loom with something home-made, so I can keep all the original bits around in case I need to revert everything at some point. I'm looking for advice on what to buy for this step, and how to plan and execute this part.
I need the car to be road legal, so all the indicators, lights, wipers, defoggers, ... need to work. Some of these are routed through the ECU. If needed, I can keep the old ECU around for these functions, but it would be nice to have just one loom and one ECU.
Stage 2: Forced induction
Once the engine is running fine under the new management, I want to try and add a cheap supercharger (I have one from a similarly sized & powered Mercedes SLK I got for 90 euros), and learn how to tune the ECU for making more power under boost. My goals here are very modest, I mostly want better low end torque. This step is just dreaming on my part for now, but might be useful to keep in mind. I might need to upgrade the fuel injectors & fuel pump for this part.