Sorry, MrPLD, I can't answer your questions directly, only give you two small ideas. In general, these eink readers really aren't designed to work as a text processor but that should not discourage you.
First, here is a long thread about ubuntu brought to the Onyx M92, maybe this is one way.
https://www.mobileread.com/forums/sho...d.php?t=217438
And in the Pocketbook subforum a member has brought vim to the reader.
https://www.mobileread.com/forums/sho...d.php?t=224559
Maybe you can ask him how useful this turned out in practice.