Thanks, everyone. You've given me lots to think about and I never even considered that making a long, skinny quilt could make it hang wonky, so thanks for those tips!
I've quilted one block with pebbles and so far, so good.
Still undecided about the borders and sashing, but I'm actually thinking I may do random short lengths of satin stitch "sticks" at odd angles here and there in white thread, to echo the sticks in the blocks. Going to try a sample first.
Watson