Again thanks for the replies.
Motors heat-up for reasons other than overload. For example, failure of the cooling fan. And pump-heads can heat-up for lots of reasons too ... bearing failure for one. So in addition to electrical load monitoring, heat sensors directly on the motor and pump-head provide additional insurance.
The old tech is robust. The relays will get activated only if there is a problem ... hopefully, not very many cycles for them. Further, the plan is drawn-up, and the relays are on the shelf. I use computers and MCUs when needed ... not here.
There is very little suction head. The water is drawn from a pond, the surface of which is less than a meter lower than the pump. Pump is two stage centrifugal.
And both loss of prime and the flow switch are needed. I won't go into all the reasons. But one is that because the pump is pushing water into pressurized tanks. Flow goes down as output pressure increases. So the flow switch opens before cut-out pressure is reached. In addition, before the pump starts, the flow is obviously zero, but it's important that the pump have prime before it is started.
I'm still struggling with the circuit for the flow switch. At very high flows, such as when a fire hose is being used, the output pressure drops so low that the pressure switch safety shuts-off the pump. At this point, the flow switch needs to substitute for the pressure switch. On the other hand the pressure switch needs to rule at the beginning and end of ordinary pump cycles. The circuit itself will be easy once I get the logic right.
Mike in California