I would not quilt it less than what the batting recommends. It only takes one time through the wash to bunch up the batting (might last more, but you know how I know). Hobb's is a fantastic batting. It's what I use for hand quilting because it provides great definition.
You'll need the foundation quilting that I drew out in any case. I'd start with that & see how you do. One option would be to go back in after the foundation work is done & use a smoke colored monofilament on top & the same grey cotton in your bobbin as before & quilt in between with the mono so you get enough quilting. That's probably what I'd recommend. You want to be sure to buy a POLYESTER mono as it is more flexible than nylon.