First of all, I absolutely LOVE everything about what you've done so far!! I've been looking for a pattern like that to do recently- great look. I think I may quilt it a little differently- maybe the background pieces or apple core looking parts, just echoing the curve large to small, but you would really have to plan which ones. Then fill in other necessary spaces with whatever you think, but the circles are so cool already, making them pop out more with quilting around them may be a fun and different accent.