This project has stalled a bit unfortunately.  But I wanted to put a link here (to remind myself if nothing else :)) to investigate the G5421CQT1U.

This is a $0.12 chip (in qty 1000) that seems to replace some of the functionality needed for the LiFePO4wered/ESP32 that was implemented as separate parts.  Since it needs 5V, it unfortunately still would require the SGM4552YN6G for level shifting the low voltage PWM signal from the micro and the AP7383-50W5 to regulate a 5V power rail, but it would integrate the functionality of the NCP81151 gate driver and the AON7804 dual MOSFET into a lower cost part with slightly lower RdsON (20 / 18 mΩ vs 21 mΩ typical), and I wouldn't need to use the wonky zener diode arrangement to make the NCP81151 do zero cross detection since the G5421CQT1U has a pin to enable that.

I haven't dug through all the details yet, but it seems to be a part to keep in my power conversion toolbox.