>>291200305
Right-click the current scene, add new scene, it will create an untitled scene. Once you've done that right-click the first scene and unload, now your current scene should be the untitled one. Once you save you name it.
>How important is it to keep all models in separate scenes?
Don't really know, I just do it because I like having things neat and easily organized. Wouldn't surprise me if the vrc avatar descriptor would choose the wrong model or something like that.