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People have differing views on the thermocouple position, as you've noticed. However, if you run the pump whilst heating (many have a control system arranged so that you can't run the heater unless the pump is running ... not quite sure why), then it make little difference as the temperature will be the same over the height of the processor and around the pipe circuit.
If you don't run the pump, the heated oil will rise in the processor tank making the top the hottest point, so with the thermocouple at the bottom you won't be monitoring the highest temperature.
My processor has the thermocouple fitted in the immersion heater pocket and it's worked fine for six years. So long as you are aware of how it behaves and understand how to work it you'll be fine.
The other point to bear in mind is that if you mount it higher up, you may be limiting yourself to only running full batches.
For the float switch, you really need to put a meter on the contacts to find out how it behaves in each orientation. The safest way to arrange it is to have the contacts open on falling level ... that way it will be fail safe. You will have to arrange your control circuit to suit.
