You could also answer all the questions in 1 post, just click QUOTE, then reply.
You shouldn't fuse it at 400 amps, because most 0 guage wiring can only handle 300 amps.
I just saw you have 2/0 guage wiring, i think you could use it without any problems.
Every time a circuit breaker trips, you need more amperage to let it trip again.
example: you have a 300 amp breaker, first time it trips at 300 amps, next time at 305, next time 310 or even more.