Thank you so much, Nick and Tom. The schematic is EXACTLY what my brain needed to make sense of this.
Justin did indeed say that I did not need diodes with LiFePO4 chemistry batteries. However, Jason and E-Bike Kit who sourced the batteries thought they were a good idea. For the amount of money...
OK, first off I work in medicine and have a degree in English literature, so I know little about electronics. I've read this thread but see directions for two batteries only and am too ignorant to extrapolate to more.
I have four 36V 10Ah LiFePO4 batteries arriving tomorrow from E-Bike Kit...