For me, it helped me to look at open source hardware like adafruit's.

The Mini Sparkle is a 4 layer and available on their github https://github.com/adafruit/Adafruit-Mini-Sparkle-Motion-PCB

There are many more available at OSHWA : https://certification.oshwa.org/list.html

I also did forget to mention, but this project is OSHWA certified too :D

https://certification.oshwa.org/ca000068.html