Just an update, I searched high and low and couldn't find any convenient way to do this, so I did end up doing it by hand.
In case anybody else needs to know: to answer my own question about syncing to other devices, I used the same file structure on each device via calibre and used FreeFileSync to mirror
Code:
*/metadata.epub.lua
from the primary device to the other two. If you have pdfs, their info will be stored under metadata.pdf.lua and so on (thanks to
jonnyl2 on GitHub for verifying where the "completed" information is stored!)
It worked like a charm between my two Kobos, and I assume it will work for my Boox when I receive it as well.