I don't really have the space for a 50 gallon tank. I think several 5-10 gallon containers would be more doable. Those would at least fit in the garage attic.
Thankfully, ours is a regular gravity feed system. No power needed.
All I was really hoping for is a single recharge of the 80 gallon pressure tank. If the power is out much longer than that, I would probably look for other options (motel, etc.).
The 1/2 HP pump doesn't need much power, but as you said the startup surge can be three times that, increasing the size of the inverter or generator needed.
Our pump is in a well house that has it's own power supply (not connected to the house). I already wired the pump with a plug I can unplug from the wall and plug into another power source. All I need is the other power source. :)
Anthony Watson