This is much classier than my "case"—I like it a lot!
At least for me, with a Pro Mini, it could run perfectly comfortably off the current from the mouse port (at the same time as a Floppy Emu, so). In fact, my Minis don't have a USB port at all, they use a separate breakout board for USB. Though you might need it for the keyboard side of your project...
There used to be ImageWriter drivers in GhostScript. You might still be able to get them to work: https://stackoverflow.com/questions/58348378/ghostscript-how-to-include-the-apple-imagewriter-drivers-it-used-to-include links to a notarised build of an old GhostScript that contains those drivers.
Or if you only want to print text then it will just do ASCII printing IIRC.