Thanks for posting this,
@MrVivekB! This speaks to me as it's identical to my scenario and how I've evaluated my system. You've done great digging in to the data!
I have an 8.55kw + 1 Powerwall system for backup only, like you mostly worried about a prolonged outage due to earthquakes (we're not at fire risk), and set my "bare minimum" at 6kwh/day with "some comforts" at 12kwh/day. Our normal non-high wattage appliance usage (oven/dryer/EV charging/AC) is about 24wkh/day. We did not opt to back up any of the high wattage appliances so if the grid goes down those won't work either. Our system produced 8,386kWh last year.
I've fully integrated my Powerwall with my z-wave home automation via Homeseer. During an outage when we're not home lights and appliances will turn off to conserve power (IFTTT rules keep track of where my wife and my phones are - if we're gone the home knows). Super helpful to know if we're out of town when the power goes out.
If there is an earthquake in the summer, late spring, or early fall we'll be fine. Outside of that time I realized that we'd only be able to last a few days and needed to augment the system. To that end I purchased as 1250w pure sine wave inverter harness for my 2018 Volt which I can use to power anything within extension cord distance of the garage. This is just to load shed things like the tankless gas hot water heater, garage freezer, and some first floor appliances from the Powerwall to extend it's runtime. I estimate between a full Volt charge and a full tank of gas (which it always is - I never use gas for my commute) I expect to get about 100kwh usable 120v power out of it after conversion losses. Also I can charge the Volt 18.4kWh battery from a level 1 charger during an outage from excess solar production during the day, effectively operating as a second Powerwall.
Finally, most of our cooking could be done with a microwave but we also have a camping stove and a couple of gallons of white gas which should last a long time properly stored. We should be good for many weeks if there's some sort of disaster - quite a good feeling.