Very pretty quilt!
How close/heavy do you want to quilt?? If you want to do a lot of quilting .....
I think I would handle it like I would handle a sampler quilt and treat each 'block' differently. I'd try to mix curved lines and straight lines as much as I could.
Check out Leah Day's site ... thinking designs like Swirling Water, Desert Sand, Ocean Current, Pebble Paisley, Fiery Commet ... in some rectangles, and straight line designs in a few of the others to break it up/mix it up.
I would put a circular pattern in the square patch blocks - something like her Sea Oat Flower.
I would SITD around the black bars and around the square blocks in the borders.
The borders I think Leah's H2O design of lines with circles would unite everything together.