I can relate to schematic issues. Having done 4 engine conversions in my van over the 30 years I have owned it (currently SVX powered with a Vanagon 5 spd--beefed up), it is confusing. But my solution was to photocopy all the relevant?pages that SHOULD apply, and make my own schematic book. I also taped the?pages together into a long strip so that its a lot easier to follow a connection, especially the fusebox?connections at the top. Then I can make changes to the drawings. But I still have to refer to the manual occasionally. Eventually I traced down every wire in the car and put it all in an Excel spreadsheet, listing to-from, multiple connections, wire colors, known function, fuse number, etc. I could do this because I rewired the whole van from 82 to 89 wiring.? It's been invaluable.
As far as the ECU tuning question, I have considered going to an aftermarket ECU, but watching the travails of various Subaru Youtubers, it seems more trouble than its worth. Perhaps the stock ECU can be reprogramed--not sure. The Stock?programing is more for emissions than power and economy, clearly. I eventually was able to obtain a JDM ECU for the SVX, which has a more aggressive map. I'm very happy with how it runs now.
Congrats on completing the project (altho its never really complete!).
