When coding Arduino projects for other people (and myself) I find having ASCII art pinouts of the hardware very helpful. It allows me to very quickly see the pin assignments and pins used. Please feel ...

(add after the "# Adafruit Feather STM32F405 board" section).. That's all. So on the arduino IDE, on the boards menu pick the option "Generic STM32F4 series" and the board part number: suboption pick ...