if I have 5 characters in a scene, all with their own materials, I have to combine all of them in one massive node tree with Mix nodes?
No, don’t confuse those two examples I gave. Each has its own Material, so each has its own Node Tree.
with your example, the two monkeys have the same UVs
No they don’t, I even gave the UV maps different names to make that clear.
What about two different objects like a cube and a sphere?
That is why I added the Plane, so there are different Objects. Each has its own UVs and its own UV Map, even when they are named the same.
When you create a. new UV map from the original, doesn’t Blender copy the new layout from the original?
Yes. And then you can change the second UV Map while the first stays the same.
