Thanks for writing this very large tutorial.
I saw this contradiction:
In the Off position the sliders are pulled to GND
I think this is backwards.
If you are doing SD card access, the sliders must be in the pull-up or off position (away from the outside of the board).
When the sliders are in the ON position (towards the outside of the board) they are hard-connected to GND.
===== My look at the schematic:
slider OFF position: DIG16 is pull up to 3v3
slider ON position: DIG16 is wired to GND
It would be nice to have part of the schematic pasted in these sections.