Wow, that's totally amazing!! You are a very talented lady. I think puttin in any type of stitches will alter the look you are trying to capture. I honestly don't think migrating will be an issue since it's only going to hang. If you ever do wash it, I'd opt for putting a few basting stitches in the large areas to hold it and then I'd soak it to wash and rinse, roll it in a big towel and gently squeeze out excess water. Then, take out the basting stitches and dry it flat like a sweater. If you feel compelled to stitch, I'd take a few stitches from the back and only catch the batting and backing together. Good luck, it's a work of art!!