The final destinations of my models will be in unity, maybe I use Mixamo.
I dont know how the software mixamo from adobe work from behind the scenes, but maybe is not to worry about this, the tool generate rig and animation for your models. But for unity:
1 - the unity use left hand system.
2 - I need to export separate models. In some games the object will be generate with random system, then I need the one file for object. Unity have the concept called prefabs, then, if I have separte part of my object in scene, I will mount many structures with the little parts and group them with a prefabs.
3 - The model need to be closed completly and the normals must be in the right position.
Mixamo: https://www.mixamo.com
Unity: https://unity3d.com