Mine did that and left me stranded in Waitrose car park.
If you can try a tow start and see if that helps.
Also a failing starter can affect the cps which means it will turn over a lot before starting and put the eml on.
Solenoid kit did not fix mine, the brushes were shot and the windings (?)...
You can get rivnuts with a closed end so, in theory, there is less chance of the threads getting water in and rusting up. You would need to be more particular with the length of bolt you use though.
Yes, take the mounting plate off, deal with the rust and fit some rivnuts in the original holes. Then bolt the mounting plate back on and then the filter housing.
There is a locking tab on the side of the injection pump to lock the pump timing before removing. Set the timing correctly,, undo the bolt remove locking tab and tighten the bolt. You can then remove the belt and pump.