First of all let me say, great work, I have the exact same case and it was a breeze to set up thanks to you.
May I be greedy and ask how you got the now playing and progress bar on your screenshots?
Just wanted to come back and say that since posting this, I've delved into doing it myself and learned SO MUCH! A tinkerer's dream!!
Once I realised that the design layout/gruntwork was done by Pillow, I started making it look pretty: I've got a little boot logo and everything! Then I got into the JSONRPC calls. Between this forum, the depth of info over at the KODI wikis, some Python refreshers and no small amount of "docker restart argon-oled" I now have my little OLED screen looking a million bucks. Thank you again chaosen3! You got me set in the right direction! I'm certain I am doing any of it in a resource-intelligent fashion, but I'm beyond stoked!