Gonesouth, I have never heard of a tankless heat pump water heater (doesn't mean that they don't exist). If they work at all like a regular heat pump, it won't make very hot water.
Roof heat pumps work until about 40 or so degrees. If you are in frigid temps, you will need something else to keep you warm whether it be a gas or diesel fired furnace or electric heat of some type.
We have a tankless water heater for our shower and a 20 gallon water heater for the coach. We also have a diesel fired Espar 83,000 btu furnace that is amazing. Also 4 roof heat pumps and 4 zone heated flooring..... so, we have options!
MM.