Your block is gorgeous!
Pardon my ignorance, but I have a couple of questions.
What is 'burbur' ? Evidently a very heavy fabric?
Are you planning on a quilt as you go .... quilting each block separately?
Do you mean for the serpentine stitch to be all the quilting you are doing? Holding all three layers of your sandwich together? Or will there only be 2 layers...front and back with no batting because of the weight of the backing fabric?
I do think the serpentine stitches you mention will certainly help support your seams. But... do you think they need that support?
Sorry, I don't quite get it yet. I am really interested in other responses too.