TomGeorge:
Hi,
You are calling it an "E Switch" is that an EMERGENCY SWITCH?If so then forget about any electronics in the "E Switch" circuit, check what you can get in a proper switch and if needed a relay.
Any EM-STOP I fit is purely mechanical and in the live/positive supply line.
If you wish to isolate the entire system, fine.
BUT
You must isolate the positive of the supply, in your configuration, if you isolate gnd, you MAY disable all features, BUT the circuit is still at full positive battery potential with respect to gnd.50Vdc shock is not pleasant and can be capable of 1mA needed to cause lethal harm.
Tom...
It's just going to be used to turn the system on and off externally from a small switch.
I want to predict millions of cycles maintenance free for it and it needs to be super reliable.