piepatch

I would definitely back all the denim squares with something. Any quilting cotton or flannel will do. You can do without the batting when you are using denim, but I think the quilt will look nicer with a backing, and the fringe will as well. I would also consider taking a little wider seam, at least 3/4". You asked if you should stitch twice, and I always double stitch the rag quilts, especially around the outside edge, but while that is the way I choose to do it, it is not required.