If it were me... (I live off grid)
Also get a 100 gallon (or 50 whatever you can afford) and ONLY run it on propane. Don’t use gasoline. No shelf life, no worry about liquid fuel, and propane can be used for back up heat and run many of your appliances, including a refrigerator. Or if you can, convert everything to propane (clothes dryer, oven, stove, central heat.) You will want a transfer switch so you won’t have to worry about going outside to plug it in. And with an electric starter your electrician can probably tell you if it can be used to automatically start when power goes out.
12500 will run just about everything you need but not all at once. The biggest draw will come from central heat or AC. For an example a small portable electric heater will take 1500 of those watts. Not sure what your central heater takes but that is easy enough to look up by just a quick look at the circuit breaker. Probably 8-10kwatts. A modern refrigerator barely uses any power. Here’s a link for some wattages
https://prosconsshopping.com/average-wattage-for-household-appliances
Bingo on all that you said! Larger LP tanks are a serious backup to NG, and gasoline.