I think that is a very cool top - congrats on a novel and beautiful design.
I would consider adding a border of a rainbow striped fabric if the top isn't as big as you want, but I think it will look just great without an added border. For backing I think I would go with a polka dotted fabric, just to keep the circle motif going, and I would quilt the white "negative" space on the front with different sized circles in white thread so there is a hint of texture but no color competing with the fabric circles. Binding would depend heavily on border/backing choices, for me...and I would make that decision at the very end!
Post pics when you finish it.
Alison