We also have a "split 400" with a 320A meter and 2x 200 amp panels.
We installed extra conduit between the two locations, and my plan is to make the 200 amp panel in the garage the battery backed panel, and some extra loads on the 200 amp outside. I am still trying to figure out what makes the most sense to move, but really want to have the vast majority of the house on the backup.
We currently have 2x Solar Edge 10KW inverters with a line side tap out at the outdoor panel/meter location, with 50 LG panels installed by a very high quality local solar installer, and they are certified for Powerwalls.
Current layout:
Outdoor 200 amp:
100 amp sub for 5x mini split AC units (9 amps max load each, 45 amp total max load, so it would be fine on a 60amp breaker)
125 amp sub inside the house for about half the house, almost all outlet and lighting loads
100 amp tesla wall connector outside west side
20 amp out door outlet near the pool
room to add the pool pump once we refurbish the pool
Garage 200amp:
60amp sub for 3x mini split AC units (9 amp max load each, 21 amp total max load, so it would be fine on a 40amp breaker)
Kitchen loads
the other half of the house outlet and lighting loads
water heater (hybrid heat pump based)
100 amp tesla wall connector in the garage
50 amp 14-50 on the east side of the house for tesla charging
My plan is to move some circuits around to look like this:
Outdoor 200 amp (not backed up):
100 amp tesla wall connector outside west side
20 amp out door outlet near the pool
room to add the pool pump once we refurbish the pool
Garage 200amp (backed up), this will put a heavier load on the 200amp panel, but it will still be fine:
60amp sub for 3x mini split AC units (9 amp max load each, 21 amp total max load, so it would be fine on a 40amp breaker)
Kitchen loads
the other half of the house outlet and lighting loads
water heater (hybrid heat pump based)
(Downgrade to 60amp breaker?) 100 amp tesla wall connector in the garage
Put these two together on a 125 amp breaker in the garage:
100 amp sub for 5x mini split AC units (9 amps max load each, 45 amp total max load, so it would be fine on a 60amp breaker)
125 amp sub inside the house for about half the house, almost all outlet and lighting loads
50 amp 14-50 on the east side of the house for tesla charging
possibly replace this with a piggy back tesla wall connector on the east side of the house shared off of the 100/60 amp tesla wall connector in the garage.
-Harry