THANK YOU SO MUCH FOR THIS GUIDE. idk if you know this but it's currently the second result on google for "renpy layered sprite" and it was exactly what i wanted to see, sometimes ren'py's documentation just makes my eyes glaze over lol
Edited to add: if you use drawing software that doesn't allow batch export of individual layers, you can save as a PSD and use Krita to do it! it will even folder them for you.