The artwork you've created looks marvellous!!
"The Empire strikes back" is a story about the power of the Empire, represented by star destroyers and AT-ATs. As it is brutal and simple (like the cue "battle in the snow") too many elements on a poster distract from that power. However the score has a variety of themes: Theme's for Darth Vader, the Force, Yoda, Han Solo and the Princess.
Variety or simplicity? I would choose the latter, less is more.