@StonedEdge use the old trick of storing the characters in the Font rom, like old Japanese computers did (MSX/NEC PC88/NEC PC98/Sharp X68000). Of course, the display may not have the resolution, but it would be a neat trick.
I have noticed an issue with the OLED stats display which still noot working when the Pi boots up.
Without an actual display, it's difficult to diagnose. But, since you created a service unit for it, why not look at the error messages logged by the service to see what's the error printed by the script ?