No 7 car garage here . I am doing some research for an older couple that moved here, to tenn, from up north. They bought a huge log cabin up in the mountains, where power outages are quite frequent & an ice storm would take out power for weeks! Thanks for all your help
We use a wood stove up north to help save on LP. A wood stove can heat a lot of area with a reasonable amount of wood (we also have a fan on, on the forced air system to help move it around). Adding a wood stove to use instead of the heat pumps might be a viable option for when the power is out. Your generator requirements would be much much smaller if you didn't have the heat pump.
You might also consider a 2 generator setup. One pretty small one, say 3KW - 5KW for some of the basics like lights, fridge, microwave, then a larger unit that can run on demand for the heat pump, dryer, etc. This would save a considerable amount of gas. They also make dual / tri fuel generators now that can change between natural gas, LP and regular liquid gas. One of these might be nice if there was the potential to run out of LP, then you could switch to regular gas for a while if necessary.