So thanks to your pointers and a few days of experimentation and trail-and-error further, I have something which works to my liking! I can create a new plugin in the editor, generate a Pak-file, and have the game pick it up automatically just by placing the Pak-file in the correct folder. Awesome, thanks a lot!
I’m still fuzzy on the final piece of the puzzle, which is getting my editor in the hands of potential modders. I get that there is the license to consider, but right now I’m just interested in understanding how to complete the puzzle technically.
Assuming that my potential modders have the launcher and Unreal Engine installed, what do I put up for download so that they can open up an editor of themselves, create a new Blueprint derived from one I provide, and build it as Pak-file to drop in my installed game’s content folder?