If the specialist says the canned goods are okay, it may be worth giving them a good wash with warm, soapy water before opening. The can opener blade will bring the stuff on the outside of the can to touch the food inside.

This is all assuming that there has been some level of smoke and/or heat penetration. I have seen some bad places, so without knowing what you're going back to, I always err on the side of caution!

If your house is sealed, great! There may or may not be some small openings to allow the house to breathe a bit. I know I do in Australia. I don't know your set up for central air, but I've got central heating and both central AC and split system. All have openings outside, so depending on what filters you have in place or wind direction blowing particulates and ash around, ask how best to flush/clean it without contaminating your house insides.

Water pressure - sinks, taps, tubs, showers. Let it run a few minutes before using. It may have been turned off or may have dropped while you were gone.

You may also have a boil water notice placed on the area. Buy bottled water before you go home. If you have electricity, have a kettle.

Do you have electricity and/or gas? Gas may be shut off temporarily for safety reasons. I imagine authorities would have checked before letting people go back to their homes, but just be vigilent of gas smells in and around your home.

Bring what flashlight, and emergency things you have. You may or may not have disruptions while things get back to normal.

Wear mask (and gloves if it's thick) when cleaning. The soot/ash will have settled everywhere, so depending in what authorities have recommended, you'll still want to protect yourself when you're washing the outside of your house. Maybe keep an eye on the weather forecast and pick the sides of the house on the days carefully until good AQ is consistent. Spray affected surfaces down before scrubbing to keep the airborne-able stuff from flying around, and easier to manage.

Keep an eye on utilities and government websites to stay updated on everything. They know your area better than I do, so I can only speak generally about things.

There are too many acronyms in your response (NAS? UPS?), haha but I get the gist of it. If you're unsure about the freezer food, I'd throw it. It's not worth getting sick over on top of everything else you have to manage right now. Health services might be overwhelmed, shops may not have the medication you need, and who knows what the road is like if it's bad enough to need an ambulance.

I'm typing stuff as I remember them (wrote the other reply when still groggy after nap), so I may have more through the week, if you'd like me to keep responding!