Your quilt is stunning. Please share the name of the pattern with us.
As for quilting... I agree with some outlining of the big blocks with the flowers, but I would stipple around the circles just catching them around the edges of the circles. This would make the background lay down and the circles seem like they were floating. For the plain small squares, I would start just in from each corner and make a circle inward. Let's see if I can make this keyboard show you.
) ( Pretend that's on the top & bottom too. Or, maybe a simple flower or leaf pattern. For the 4 patches, I would do a squiggly circle starting in the center of a small swirly in each block. Swirlies, or curls, as Charisma calls them, in the larger square blocks would look good too.
Your pattern is so dramatic that I wouldn't do any type of going from corner to corner in a straight line. You know, like an X That would take away from the wonderful design of the quilt.
If you have a clear see through piece of plastic or a Saran wrap type, put that on top of your quilt and making SURE that you don't write on the quilt, draw out what you think you would like to do on the quilt and see if you like it. This small step is how a lot of really good long armers started designing stitching to go in blocks that would enhance the blocks and not take away from the beauty of them. I would suggest a Washable marker and write on the clear paper, TOP. That way you won't accidently turn the clear paper upside down and get marker on the quilt. I have read that some quilters, tape the clear plastic wrap to their quilts, and stitch through it, tearing it off afterwards. Please test this on some extra fabric before you do this on the real quilt.
The Clear page protectors that we sometimes use to put our patterns in would work for designing your quilting too. Draw your block on the paper, then play. Leah Day has so many wonderful free quilting patterns on her site
http://freemotionquilting.blogspot.c...on-filler.html Keep in mind, too much quilting could make your project a bit stiff. Sometimes, less is better.
Have fun!
Barb