I'm glad you're enjoying Decker!
I greatly appreciate it when users share Decker with new communities and people; I can use all the help I can get to spread the word.
Getting Decker working on epaper tablets sounds like a challenge, but I think it would be a wonderful fit. I don't currently have any devices I could use to test/develop such a port, but if anyone is up for experimenting in their own fork, I'd love to hear about it.
You can indeed copy and paste cards between decks, and even between native-decker and web-decker. Cards copied to the system clipboard travel with any prototypes that are referenced by the card, but if a card references any custom fonts, sounds, modules, palettes, or deck-level scripts you'll need to import those separately. If you're comfortable with a command-line, you could write Lilt scripts for automating cutting apart or merging together decks; Lilt has all the same APIs for manipulating Decks that Decker itself has, and it can also manipulate multiple decks at the same time.
I can't reproduce the mouse cursor/canvas input issues you report for native-decker on Windows. I test and develop those releases on a Surface running Windows 10, so it's possible the problems are a regression in newer Windows releases or something strange about your OS-level settings for pen/touch input. I'd recommend fiddling around with your control panel. If any other Windows users are having similar issues, feel free to chime in.
Being able to press delete/backspace and remove rows from listboxes in various dialog boxes throughout Decker (including the prototype list) is a systemic bug; grids weren't properly respecting the "locked" setting. This is patched in the source repo, and will be fixed in the next binary release, along with a number of other native crashes I've tracked down.