I have designed a schematic for a PCB for a doppler sonar project. The plan is to use a RPi 3B+ for some basic signal processing, an arduino to produce a 40 kHz wave via PWM which is filtered to produce a 40 kHz sinusoid, which is transmitted after a Tx circuit, and then received through an Rx circuit, sampled with an MCP3008 to the arduino, which will send data to the Pi. Im using 2 x LiPo batteries in parallel to power it, and have a battery charging circuit included, to charge them in parallel. I've used a nMOS to switch off the main circuit when the batteries charge (when USB is plugged in, circuit is off).
With that context, are there any glaring issues with the schematic that I should address before making the PCB? Specifically the RPi powering circuit and the circuit turn off while charging circuit? This project is purely for fun and learning purposes. See images attached (in the order they appear: Overall circuit, RPi powering circuitry, circuit turn off when charging, battery charging circuit).