Do you need 100 amps from the alternator? Will you be using enough power to require that charging rate?
I believe 2000 watt inverter is too large for a vehicle powered inverter. Be aware that a NCV3 has an automatic electric air heater that uses about 900 watts of alternator output when it is operating. Electric air heater turns on when dash controls are set for heat and engine is cold. Turns off when engine water temperature is high enough to provide heat. As I recall it shuts off around 140 degrees.
I have two selector switches. First one selects real shore power or vehicle powered inverter shore power or off. Second selector switch selects charging (power to the house inverter/charger/transfer switch) or electric air heater or electric water heater. I limit the power from the vehicle powered inverter by limiting the connected load. The shore power charger is set for 40 amps.
Inverter can be run continuous if you have adequate cooling. Do not bury the inverter in a cabinet. I did that and overheated the inverter. An additional 120 volt AC cooling fan can be plugged into the inverter duplex outlet, so it runs when the inverter runs.
Both a DC to DC and an inverter have efficiency losses. Which is higher? Do not believe that is important. Doubt you can see a measurable difference in fuel economy when alternator is providing power.
Electrical | Orton Travel Transit (ortontransit.info)