Scene2D stages for 2D topdown game

Hello! So lately I was playing with libgdx and got stuck on some implementations I would like to use but don’t know if it’s a good practice to do so.

Here’s a sketch of the idea:

http://s23.postimg.org/doavtfw07/Schema.jpg

Since stages don’t have size how can I implement them in such a way? Also on what coordinates should Actors be rendered in both stages?
I would really appreciate some help…