27kw is serious overkill for a typical home.
10kw should do the job quite nicely, especially if you’re sensible about concurrent loads from your major appliances.
I’d get my pencil back out if I were you.
Agree, 10KW should be fine.
I have experience with auto-switching backup generators in commercial buildings, a whole house Generac generator and a 5kw portable set up to run on propane.
If (a very big IF) you have Nat Gas available, but that huge generator in, otherwise, go with a 10KW for your max and set up an “emergency bus” that it powers. Forget elect stove and oven, elect water heater, and total HVAC system on the emergency bus. Put several room outlets that are for window A/C units,fridge, microwave for cooking, lighting, computers and TV, and you will be fine. 10KW is plenty for that.
My 5KW will run off portable or fixed propane tanks, have some BBQ tanks and a 300 gal tank on site. This works fine for lighting, fridge, wellpump, and a window A/C.
The larger you go on capacity the more expensive it gets, cost seems to go up exponentially.