Very nice wall hangings! I would recommend you begin with a practice piece before starting in on the actual quilts.
I quilt with a 12" hoop. It may have to do with short arms, but I've had trouble quilting in a larger hoop. I think 14" is the size I've seen recommended the most. You'll have to baste or pin fabric around the perimeter of your quilts in order for the hoop to be functional when you're quilting nearer the edges.
I know from past discussions that many people hand quilt with no hoop, and that might be more convenient for small pieces like this.