DiploStrat
Expedition Leader
how would all of that communicate? would the alternator attempt to charge the starter battery first then both auxiliary batteries ? at what point would the ctek come into play?
You could do worse than to read the documents here: https://diplostrat.org/documents/
First "Watts Up?," then "Charging Up," and finally, "Doubling Up." If you are even considering a 400Ah bank, then invest a bit of time before you invest money.
Best wishes!