Wow!! That is great! And very ambitious. I would like to see a circular design in the center of each square. I love quilting on my sewing machine, with the embroidery hoop. Don't know if you have that on your machine. But with the geometric designs, I think something swirly or flowy would be good, and with a neutral thread. A beige or taupe very often blends and picks up the colors of what it is on, while still showing off the stitching. Good luck! And be sure to show us a picture when it is finished.