power transfer switch with circuit breakers
To clarify, you do not want or need a transfer switch. The transfer isn't fast enough to keep critical loads up. You run a subpanel off the output of the inverter at all times, and put the critical loads on that panel. When power fails, the only change is that the batteries stop charging and start discharging. Make sure your charger is capable of handling at least the average load of the inverter, plus about 50% minimum overhead (to account for the inefficiency of the batteries and the inverter). So if your average load is 2kW, you need a 3kW charger at the absolute minimum.
I am a lawyer, but not your lawyer. And who cares anyways? We're here to talk construction. This is DIY advice, not legal advice.