We have a large house with 2 150A breaker panels for all of the circuits in our house. One of the configurations considered for our new system, was to split our 44 solar panels and 4 PowerWalls into two systems (22 solar panels and 2 PowerWalls each), with a Gateway for each of the breaker panels.
We reviewed the 2 year history of energy usage from our smart meter - and also reviewed the circuits being used on both of the 150A panels and concluded that our peak usage was well below the theoretical 300A of load supported by the two panels.
So instead of implementing a split Gateway system, we were able to go with a single Gateway with a 200A breaker to the grid, with the PowerWalls able to provide sustained 20KW of power in off-gird mode (without any solar power). A major problem with the split Gateway configuration was that the loads weren't balanced between the 2 150A breaker panels, which would have required rewiring (further complicated because the HVAC upstairs units and outside compressors were split between the 2 panels).
After the system was installed, I ran some tests and confirmed that under a peak load (all of our pool pumps running, all 3 air conditioners running, and both electric ovens on), we were under 200A of load.
However, that configuration was using 22 KW of power, so in a worst case scenario, we could have problems if everything was on when we encountered an grid power loss - and we didn't have any power coming from the solar panels.
We also talked about the possibility of a dual Gateway configuration with both Gateways sharing all of the solar panels and PowerWalls with one Gateway connected to each of the 150A breaker panels. But even if that configuration was supported by Tesla, it would have been overkill - since we are still limited by the power being provided by the 15.4 KW (more likely a peak of around 10 KW) of solar panels and the 20 KW from 4 PowerWalls.
When we started the planning process, having whole home backup - and using all of the solar panels and PowerWalls for the entire house - was our desired goal, but based on our basic research that didn't appear likely - and that we'd have to settle for some type of split system and then dealing with the imbalance between the two house breaker panels.
But after the electricians reviewed our actual loads - we were pleasantly surprised we'd be able to get a whole home configuration with one Tesla Gateway providing power for the entire house (with the exception of our two Tesla Wall Connectors for charging our S & X).
Boltzzz - if you have smart meter data, recommend you pull that data down into a spreadsheet and look at your peak power usage for as far back as the data is available. Also, with a smart meter, you could also do some measurements on your own by turning on all of your heavy power devices and then looking at the actual power draw on the meter. It's very possible that even if you have 2 200A breaker panels, the actual load could be much less - and that you may be able to operate on a single Tesla Gateway with a single 200A breaker to the grid, and then plan for enough PowerWalls to support your actual load.