What a beautiful pattern. Does the pattern have any instructions for how to finish it? I would think you might have to put something sturdy around the top so that it won't sag.
I highly doubt that the project will maintain it's shape without batting and quilting stitches. Most Iron on appliques are recommended to be blanket or satin stitched around the edges of the applique. Most times it is done before layering the quilt, but with this being a smaller WH, the pattern directions might suggest you do it after layering, thereby letting the seam act as the quilting. The invisible monofilament thread is used by many or the Deco Bob 80 weight thread. Both will be almost invisible.
I look forward to seeing your finished project.