Setting up Git repo with other Git repo with Submodule? (WordPress development)

I have a Git project/repo called “ABC” to which I would like to add WordPress among other things.

ABC
  WordPress
  Other 
  Stuff

Ideally I would like to base my WordPress setup on the WordPress Skeleton repo.
(The WordPress Skeleton also contains a submodule referring to the latest stable WordPress release.)

How do I go about creating this setup?

1. Should I fork the WordPress-skeleton vs copy it into my existing repo?
2. How do I update the submodule that the WP-skeleton refers to from my ABC git repo?

I guess I am confused regarding the use of forks in this scenario when I want the ABC to contain code from other repos that in themselves have submodules.