One of the FMQ classes from Crafty recommends that your SID first on every seam. In fact, she refers to it as "every stinking seam" because it is so much work. The instructor would also agree with QuiltE, and use a finer tread to SID. She used "Bottom Line". Just from my experience, I have gone full circle from pin basting, to spray basting, and now back to pin basting, because I start each quilt by SID. When I get that done, everything stay put. On your quilt I would SID on the major seams across and down. Then I would do diagonals across the whole quilt. It will be beautiful. I love the placement of your colors.