Jayhawk, in the KA200 the nacelle tank is considered part of the main tank system. I don't know about newer models, but in the early 90 series KA the Nacelle was a separate tank in the system altogether. 90s referred to "nacelle" and "wing" tank systems separately if I remember correctly. 200 refers to "main" and "aux" systems.
Yes the 200 does have the tank in the nacelle, but fuel contained in there is considered mains fuel- don't believe me? Grab a manual and add up the capacities for all the box sections, wet wing section, nacelle, leading edge tanks etc and you might find that it equals the book figure for the Main system
The jet pump in the 200 aux tank is not an electrically driven pump. The electric side of things is effectively just a sensor which will see if there is fuel in the aux and if there is it will open the motive flow valve. When the aux tank empties, the motive flow valve closes and stops fuel from going through the jet pump- it does not "shut off" the pump.
I kinda think the requirement to fuel the mains first of a 200 is to prevent someone from filling the aux tanks full, but not the wings. This could cause a problem with the weight distribution in the wings.
I reckon you are correct with your first sentence, but I doubt the reason is for balance reasons.
I wouldn't think that 57 gallons in the nacelle section only (no more in the rest of the mains) would be able to draw out 79 gallons from the aux tank via a venturi! Hence why mains must be full first!