Love that pattern! You did an great job. I would quilt down the leaves and vines mimicking veins in the leaves. The flowers, I would quilt up and down mimicking the flower petals. Background, if you are hand quilting, I love the grid idea.
If you are machine quilting, I would do a meandering vine stipple on the background leaving the flowers and vines free to "pop". But then, I am a FMQ so I'm partial to the background stippling. Either way, the quilt will be beautiful no matter what you decide to do.