youme, I love the quilting. I have never seen a triple row like that. I love it. It makes it vary interesting. For the Squares have you thought of some free motion flower in each square. You can trace a pattern on to tissue paper, the type you wrap presents with pin it to your quilt and freemotion on top, tear away when done? Just a thought.
How big are the squares? Poly Batting should be quilted no more the 3-5 inches apart according to the Singer Quilting Bible, which I need to reread.
Depending on the size of the squares you might just need a small something in the middle. I wonder if you did a small diamond and then repeated it twice how that would look.
Let us know what you end up doing and post pictures.
G