Repos Production 7 Wonders Babel Game

Is this a stand alone game (or does it require 7 wonders)?

Is this a combo of both expansions "Cities" and "Leaders" or is this another set of expansions ?

For the Wonders Pack you need Cities for all the symbols to make sense. Do you need either previous expansion for everything to make sense for Babel?

Which is the best 7 Wonders expansion, and why?