Currently one skin requires 4 mods to be installed
And it cannot be installed from the game, you need to download them manually from the portal one by one…
Can't reproduce. I removed all versions of these mods (both folders and zip files) from my mod folder:
- minime
- CMH
- Pi-C_lib
- zootopia-judy
I disabled all mods, then restarted, went to "Mods" --> "Explore", searched for "zootopia", and selected "zootopia-judy". After I've hit the "Install" button in the right pane, all four mods were automatically downloaded (order: "zootopia-judy" --> "CharacterModHelper" --> "Pi-C_lib" --> "minime"). After hitting "Confirm", the game started as expected, with all mods enabled.
I then quit, removed the four mods again and started all over. This time, after installing "zootopia-judy" (which again pulled in the other mods) but before hitting "Confirm", I clicked on one of the dependencies and got, indeed, a hard crash. Is that what happened to your users? This would seem to be a bug in Factorio.
As for the maintenance problem, I think it is simpler and can be solved with a git submodule.
Even if I moved the functions from the library mod to CMH, you'd still have to download the lib mod because minime also has a hard dependency on it. And it wouldn't be simpler to use a git submodule because I'm not using git – so I'd first have to get a git account (which I don't like to), then learn how to use git, and then also learn how to write/use git submodules. Seems to be much more trouble then keeping everything in a single library mod. :-)