Decide if you need the cold weather package.
If you are running propane, you might need an extra tank to get enough vaporization to supply the unit in extreme cold. That was what my dealer told me.
BTW, my estimate was around $8-9k installed so I decided to go cheap. Bought a dual fuel Champion 7500 watt unit ($850), my propane supplier will run the line ($300) and a contractor will install a transfer switch that feeds to the mains. It will not be "automatic" but simple and affordable. I am going to build a small shed to house it, as well as a spare 5000 watt Generac gas unit that I have used for 20 years. The shed will have doors that can be left open and powered ventilation. Cost for the shed will be about $300. Total cost should come in at less than $2.5k
I really wanted a whole house automatic standby. Install and operating costs were more than I could justify. I do not need continous power during an outage and normally operate for an hour every 4-6 hours. And I did not get a warm fuzzy feeling from the local supplier.
Good luck with your install.
I've wondered about the propane tank, it's 500gal. The only propane usage I would have would be for my furnace emergency heat if my geothermal decides to go. When I initially kicked around this idea a few years back, neither to propane supplier or the Generac dealer seemed concerned.