Install a good relay and don't worry about it. GM quit doing the oil pressure switch bypass in the 90's (and I doubt other manufacturers had a back-up bypass at all) and you don't constantly find...

You don't need the oil pressure switch. It's just a backup to the fuel pump relay and there are millions of vehicles on the road that only use the relay.

The rule is never place the CTS after the thermostat. That plate goes under or before the thermostat. The only issue you might have with a plate like that is the sensor and thermostat clearing each...

Is there no threaded bung hole to the drivers side of the thermostat outlet? Most manifolds seem to have at least one threaded hole somewhere on the front coolant crossover.

Why can't you fit...

I've seen thick spacer plates you put under the thermostat that can take a CTS sensor through the side.