Quake 3 (and FOSS versions like Open Arena) divide the player models into three pieces: head, torso and legs.
So the idea has been done before and is not bad idea per se, but it does make life more complicated having to transform the pieces to match the correct position.
Quake 3 uses "tags" in the MD3 model format for this, which are vertex with direction information -- you orient the tag similar to a usual vertex and it serves as the origin for the child piece. E.g. torso piece has a standard tag for attaching the head onto.
I'm not a modeler so I can't answer your other questions.