Beautiful!
Are the pieces on the left made so you can cut them out and sew them onto the panel to make it 3D? If so, I would fuse them to a backing colour to finish the backs and then stitch them on lightly just in the centres and along the tops for the ribbons, so they stand out from the quilt.
For the horse, I would outline him and then quilt around his eye and main features like the line that runs down to his muzzle to his nostrils and his jowl, to give him some definition and do some lines through his mane.
You've had good suggestions from others about the rest of the piece already.
Watson