I see a simple stitch in the ditch that "frames" the designs; along the seams in the white area. Simple but effective, I think. Simple, yes; that's the way my mind works for quilting.

Will be vvvvvvery special, and take a pic outside for real coulors after quilting

LOVE IT!!!! The stack and whack pattern is something I have always wanted to do......it is on that long list.....

Depends on how comfortable you are quilting. I think it would nice with the plates (stack n whack part) SID and then stipple in the solid area in a color that blends well. I think that would make your plates stand out. BUT if you are comfortable doing FMQ than something more detailed in the solid would look wonderful.
What did your original fabric look like - the quilt is gorgeous