As YoraeRasante said, there's no way to do so that i know of. You could rip the assets and merge them on blender or hit "Import". What for?
You mean, automatically or just in general?
Because i only know how to do it manually by using the animation then CTRL+LClick the same animation with the other character selected then hitting "Re" with both selected.
Absolutely.
About the collection of cards, aside from Kevin2018's post, you could try the
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or
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.
About the third one, i haven't personally seen paywalled cloth mods for KK but that being said, just update through KKManager, tbh.