I've trouble shot allot of relays so I won't add one unless it will reduce the amount of wire by 40-50%.
Switching the neg side is not standard practice........best if a switch is on the pos side so it removes power from the circuit. In this case power can be removed with the switching breaker but it removes power from everything.
I always protect the coil in the relay separately from the device as (in my applications) the coil wire is much smaller than the device wire.