good news, if you’re using the gltf file format and on load using traverse() to iterate throught the model parts, you can retrieve any part of the model with simple conditional if statements, objects have been setup to be filtered with the parameters isMesh isObject isMaterial etc. hope this helps.
you would need to look into distributing parts either between scenes or layers, there are lots of resources on both this forum and the documentation on how to setup shadows such as Struggle with GLTF and lighting - #2 by Mugen87