If the motor accelerates after you stop pedaling this sounds like a problem with a torque sensor and you will most probably get a new motor to fix the issue ... Would suggest to get this problem checked with your LBS.
IMHO 18psi is kinda low for rear and your weight, I'm 85kg and my rear is about 25-27psi with tubeless tires (not Eddy Current). I use to have Eddy Current, but was not happy with them, terrible grip in damp or wet conditions and knobs were very prone for ripping off ...
I have now found this exact spare screw, it is M4x10mm indeed but it has nonstandard head and it is from ALU material which makes it pretty fragile, especially torx socket: TCU SCHRAUBE M4X0.7X10, TORX, BLK
Standard screw M4x10mm with countersunk head or socket head may still work for you if...
Yes. You just need to loosen 3 cable clamps by the shock area (you will have to remove the shock to reach one of them) and you can pull the cable out...
You search for new sensors and then you add it to data screen, you have rear gear in several different variants and the battery level (I think only 3 levels; full, half empty and near empty).
Are you sure it's M4? From memory it is smaller that M4 ... Standard torx size for M4 is T20, so I guess it should be M3x10mm T10 countersunk screw ... Can anyone confirm? (not having bike in reach of my hands right now ?)