Got to be the ECU or wiring. I know these problems can be frustrating. maybe a second hand ecu could be found on ebay or is there someone in your area with a motor the same that you could swap ECU's over to test yours.
The gearbox will self destruct without the circlip,
When I am doing a job like that I lay all the parts out on a board in order of disassembly, that has worked well until we got an apprentice that likes to move things.
Good work I can see you are highly motivated on this project. that helps a lot.
There are some issues in fitting manuals to auto Ke55's a custom crosmember may be needed try FAQ.