Hi Ken,

About the current draw from the batteries. Don’t forget you are running 6 pairs in parallel. So each battery only has to supply 80 Amps to get to 400 Amps. 80 Amps is not excessive, even for a AGM battery. It would be if you keep doing it for 10 minutes or more.
So the battery bank is well laid out for supplying that kind of current. Your starter battery has a harder time starting the engine.
The problem starts when your batteries get old. At that point the internal resistance of the pairs becomes uneven and you will see some batteries working much harder on the current draw then others.
In case of AGM batteries, keep an eye on the individual voltages of your batteries if a pair gets out of balance it may be an indication of a bad battery. Isolate the pair and see what their voltage in rest  is. Anything below 12.2 is bad for charged batteries.
For lithium the BMS should take care of balancing the batteries and very few people know what these things do in the long run.

Regards,

Arno Luijten
SV Luna,
A54-121