I think Melvin is a nice character that already has a few props like his horns and tooth, tongue. But I wonder about characters with many props, like clothes, a watch, necklace, shoes, etc. What is the best way to unwrap, is it a good idea to make a single UV map including the character's skin and his props? or should we split it and have a different UV map for the props?
Good question! Ultimately, the answer is "it depends." How will the viewer/player experience this character? At a distance? Close up? Frequent, long interactions or a single brief snippet? Will the props be fixed, permanent features, or interchangeable parts? Fewer textures will be more performant, but if that's not a strong consideration, it just lies to your own organizational preferences.