You have so many colors in your top so I think you could use almost any color you like - blue, purple, green, red, - I have found some shades of purple work almost as well as navy blue as a "neutral".
As far as quilting goes, I drew out a black and white drawing on graph paper, and then started to doodle.
You can draw out something similar or use one of the drawing programs (i don't have a quilting program) - to see what you think.
From what I've read, the high loft battings are usually tied or sent out to a long armer - and I have no idea how the long-armers feel about trying to quilt them.