Portable microcontroller based I/O expansion board

I have a basic concept for a portable microcontroller based I/O device.
I have the schematics and design data what is shown on the pictures in KiCAD format, which I can share with you.

The device consist a display, LEDs, rotary encoder, a potentiometer, buttons, some FET based screw terminals, a serial output, a light sensor, a microphone and a speaker, and a BLE UART bridge (JDY-08).
This is a 2 PCB sandwich design. It is a 4 layer design right now.

I have a mechanical concept, but the schematics contains some serious errors.

TODO:
- schematics should be checked and errors should be fixed (critical)
- the documentation of the JDY-08 says the UART is TTL level, while the rp2350 based microcontroller is 3v3. A level shifter needs to be added (critical)
- The MCU should be secured against backpowering via the secondary USB port (would be nice, but I can live without this)

The ideal candidate have experience with :
- microcontroller based designs
- can read and createelectronic schematics

This is a unique piece production, no serial production is considered.
Therefore I plan to keep the easily available MCU board.
I'd like to keep the current PCB mechanical design.

I need only schematics changes. I am able to do the PCB modifications.