I couldn't find the specifics of weather
350W was total (12VDC + 240VAC) output or just the 240 line. But assuming Honda has a marketing
dept. like everyone elses I'd bet that was total power output.
it would seem there are 6 DC coils and 15 AC, it would be reasonable to assume that you could get a maximum of 250 W of power out of the AC line. That will end up below 17A of charge into the batterys.
It seems the 12VDC line is intentioned for charging
batteries. I wonder if you coud utilise that seperatly, i.e. charge a single battery
from that and the rest of the bank from the 3 state. I can see trouble trying to couple the outputs togeather, probibly best to leave them seperate or not use the DC at all.