I would definitely line it so you won't have any raw edges out in the open. I would use something light weight for the lining, maybe even another shower curtain, that way you will have the basic size. You won't want to use any batting as that will make it too heavy, especially for a tension rod. Yes, on the quilting, that way you can keep basic quilt traditions. You can get as fancy as you want with the stitching, don't limit yourself to STID. If you don't use batting, STID will become invisible.