I'm going to let my DH answer those questions, since he's the HVAC professional. Here's what he had to say:

We originally were going with oil until we started figuring out the cost. Oil is roughly $3.50gal or more and propane is right around $2.00. We will be using a system that is basically a 3 fuel system. With that being said, it will work like you were told by your HVAC guy. Heatpumps aren't as efficient at lower temperatures because they use an electric heating element to help boost the air temperature when it gets really cold. That being said a "heatpump only" system does not produce a feeling of warm air at your vents unless the heating element is on. The propane furnace will give you warm air. Your installer can set the temperature at which your furnace kicks in and the heatpump stops. This is all done in the wiring you do not physically have to change a setting. 32 degrees might not be the point at which you want it to change over, you might prefer 35. We are also installing the electrical element that was mentioned earlier. The reason for this is incase we run out of propane or propane skyrockets in price. We are also installing a system in the basement that will heat/cool the basement and first floor and a second system in the attic to heat/cool the second floor. That will be the most efficient way of heating/cooling a home. You can install programmable thermostats so that you are not running systems in the areas you don't need to. The Honeywell 8000 is the model of the thermostat not the equipment thats being installed. I also saw on another post that you are planning on using propane for cooking and fireplace. Check with your plumber on installing a propane hotwater heater. An electric hot water heater is the most inefficient way of warming your water. I also saw you were quoted a 300 gal. tank. Check with your propane company if that is going to be large enough. We were quoted a 500 gal. tank and our home is 2200sq ft. The tank will only be filled about 80% so in your case roughly 240 gals. versus 400 gallons.