The way UVmapping works, scaling down a model to match the mice shouldn't have any effect on the textures. But, the size you have some items, filling a large chunk of the scene, they need a texture of similar size to the final image. Or bigger. It's the size relative to the final immage that matters. You do have to be careful with procedural shaders. Something that looks right at human scale can seem coarse at mouse-scale. Again, it's a final image effect. Once the detail generated by the shader drops below the final pixel size, it starts to look the same. But this is like one of those "what is it" microscope pictures.