Is it okay to stack UVs?
Substance will update your stacked uvs every time you reimport the mesh from Edit>project configs. You can offset uvs for baking and then reposition in 0-1 post bake. Or you can just clone geo after baking. Either is fine.
Are overlapping UVs OK?
There’s nothing wrong with UV maps overlapping. Depending on what you’re looking to unwrap, you may wish to use Cube Projection, Sphere Projection or Cylinder Projection instead of simply UV unwrapping by default. You can find these options below “Unwrap” in the “UV” dropdown. You may also wish to use Smart UV Unwrap.
Can you use the same UV map for different textures?
You can still use the same UV map for the material textures, but since you’re using different images in those textures, the UV islands can overlap. In other words, if you have two eyes and a nose in the same mesh and you use different materials for each, their UV’s can be on top of each other if you also use a different image for them.
What do you mean by ” multiple UV maps “?
What do you mean by “multiple UV Maps”? Probably you want to define the “texture faces” of your object. Where each of the (maximum 8) texture faces is mapped to a different 2D image. If you want that, then (in blender) you must use one material for each of your texture faces (as i show in my video).
How do I pack two UV maps into one?
Easy enough to do in most packages. Pack the maps using your favorite texture editing app, Photoshop for example. Put two 1024s together into one 2048×1024. Then adjust the UVs to match. Scale each 50% on the U axis, and reposition each on U to match the texture. Create a material, load the packed maps, assign to both meshes.
How do you use multiple UV maps in Blender?
They both do the same thing, which is that they show material assigned image textures and shading. The image gets painted on, since you’re using texture painting mode that directly paints on an image, just isn’t displayed properly. The object also has unapplied scale. Ctrl+A -> scale to apply.