I'm thinking... maybe the moon shouldn't have such a large & bold face. The stars already add so much, you can tone done the man in the moons face a little, maybe.
And maybe gray-out the teepee (it's not one of the main images)- we'll still understand that it's a teepee.
I love how you have done the trees, and I love that horse- maybe not hide his hind feet? his tail is perfect!
Heck- why not make the person on the horse a woman (she could have longer hair that sort of tangles with the horse)
Sorry, rambling only because I LOVE this idea so much. I'd wear it! ;)