Electrical – What’s the minimum amount of electricity used by an appliance

That is fundamentally correct for the time the lights are on, yes. It will depend on the specific LEDs and ballasts chosen (the ballast may or may not be part of the fixture, and some cheesy outfits try to give the lumens per watt INTO the LED itself, ignoring the watts wasted in the ballast converting from AC to DC.)

@Tester101's "wire heating" strawman (in comment) would still be affected in the desirable direction (less amperage draw for same light = less wire heating), and is insignificant for any properly sized and constructed wiring regardless of light fixture choice.

Lumens per watt of LED fixtures vary widely, still, and there are definitely still fixtures for sale which seem to be built on the belief that buyers will see "LED" and think "very efficient" without actually delivering good efficiency (inefficient LEDs presumably being cheaper than efficient ones).

It is very unusual but not unheard of to have a furnace hooked up to a heat pump. Usually you would have an air handler and air handlers usually have backup electric heating strips. These heat strips Combined with the 300-400 watts from the blower could easily suck 1700 Watts. The strip heat should not be on when the fan is set to on and the temperature is turned down but it is not hard to miswire the unit. You should also verify the heat pump is not coming on too as this is not too hard to miswire either.