Oh dear this IS some investigative work!
I confess I love forensic files. There is always some clue somewhere, and many times the most likely suspect is the actual killer
So, I think the issue with the tank comes from the malfunctioning TURBO, it was toasted (back in 2015 or 2014 when I got the car) because of that and the UBER complicated amount of systems of this type of car, any Car technician working on it would never figure out.. anything in fact. All peripheral sensors were broken (coolant thermosensor, knock sensor, thermo switch, O2)
As per the ECU being burnt, my thoughts are with a short circuit, and most probably the harnesses of the injectors. One of them smoked badly at one point and in the end I remade all 4 injector harnesses (and a second burnt computer)
That wire of the pump (the shielded wire) was tampered with, here my dad gave me his 2 cents on that, because he knew about PWM, signals, noise suppression and more from his telecom times. The person who tampered there did not know about this and thought a ground point was needed for the fuel pump. But instead, it was a clean, unclogged fuel line what was needed. However, in splicing the negative wire and attaching a lead to the chassis, this would "send loose" the signal to chassis rather than the pulse control as ground coming from the ECU. (A potential additional problem to the ECU)
The body work, yes, this car was in a colilsion, front end and sides, mainly the LHS rear panel. ..
What a true investigative work. And Im not done.
Below is a crude representation of what is inside the fuel tank. That blue pipe ends in what I call the suction structure, right at the back of the tank, where all the debris collects especially if the car is in a nose-up attitude. This will be examined thoroughly tomorrow after washing well the tank and cutting an opening safely.