Star,
That is really pretty so far. I will take the time to interject two things from a long time of personal experience.
First is a real simple at this time. I suggest that you flip that single small feeder from the positive post over the divider to the input (or output) side of the 300 amp breaker. You will most likely never have to mess with the batteries in the daylight on a nice day and if there is more than a single connection to a battery post, it can be done wrong. (The 4/0 don't count because they are like bending pipe.)
Next is another based on experience. Get a label maker. Label every wire that you know what does, even if you can see both ends. The is will save your bacon at some point and then you will be glad you did this.
Matt