I have seen the heater use as much as 4.5 or 5 kW. When the AC button is turned on, the energy use can rise another .5 to 1 kW. I don't know if this is because it increases the power to the heater or because the compressor actually runs at the same time to defrost.
The compressor actually runs at the same time, to dry the air. In the "hybrid" system, when heat and defrost or heat and A/C are both engaged, the heat pump provides the A/C and the PTC heater provides all the heat. That makes the combination a real energy hog.
I don't believe Leafs after 2012 have a heating liquid loop. I believe they have a direct PTC heater. This may cause the behavior to change.
Correct. From 2013 on the heating is all direct to air - no coolant/heatant loop other than the one inside the heat pump.
Finally, when the car is plugged in, it will not exceed the input power from the charger. On L1, this is around 1.5kW. L2 is 3.3 kW or 6.6 kW depending on the on board charger. Heat while plugged in only works if the car has a climate control temp timer enabled and the car is started by holding the brake while pushing the power button or the climate timer triggers.
Hmmm... My understanding is that the car will draw full heating power, because all Leafs power their heaters and A/C or heat pumps directly from the battery pack. The power provided by the EVSE will either fail to match the power drawn, resulting in dropping charge level, just match it (no change in charge level) or will exceed it (car keeps adding charge, albeit more slowly). I know this. The only thing I'm not certain of is whether or not the coolant loop systems in the 2011-2012 cars have the heat-limiting feature you mention. I know that 2013+ Leafs do not.