It’s probably much easier to just add the lists directly, without having to copy and paste the contents-- however this is completely your choice! If you find it’s too unmanageable or annoying to have too many individual lists, I would go with compiling a large one by copy paste.
One thing though is that if you keep the lists separate, you would be able to single study a list at a time pulling just those list’s words for review as well, versus if you compiled a large list where single studying that would show any items due for review from the entire large list.