I also have had success with the serpentine and other wavy stitches when I want to jazz up a quilt without fancy quilting.
I'd probably do 3 lines per block and 1 down the center of each sashing strip.
Keep an eye on your bobbin thread. I'm always surprised how fast quilting uses it up!
Once you wash the quilt, you probably won't notice the vertical misalignments. (I don't see them even though you pointed them out.) There's always a magical transformation when that beauty comes out of the dryer all crinkly and soft.