I'd do the pinwheels in subdued hues of the colors in your feature fabric, so as not to take away from the fabric - and use the feature fabric for a wider border. I'd do 2 borders, one in a sandy color (narrow) and the 2nd, wider. I'd do sashing from the sandy color, too, to separate the pinwheels. Love the fabric. Am working on one right now with the Oregon landmarks and features, its black with lovely colors in it. It's a challenge using the fabric in such a way that you maximize every inch, so I know what you're going through! You might try to find more, to use for the back, if possible, since you love it so much.