Your banner looks cute, it seems a little barren on the far right side, but that depends on the art style. Simplistic art tends to be hard for me to give feedback on, hah. It's nice that you have it custom-made.
As for the thumbnails, have you considered changing the template up? Like having somebody draw you a PNG transparent machi, to show off in different poses on the side of the thumbnails? Including the free download tends to take up viewing space on the picture. You can try formatting some new designs for thumbnails ^^