If that appliqué work is anchored with machine stitching on the edges I would do some various stippling in backgrounds I.,e., micro stippling,echo,and McTavishing some parts. But, also with a matching thread "lock"down some of the larger appliqué pieces so the don't "bubble" up when finished by say just a gentle outline between two parts of whatever it is---like outline bird wings. If those app-pieces are merely fused down I would want to straight stitch on the very edges before quilting it. In those sashings I would do some sort of simple design like a leafy vine or swirls just so they too lie flatter and don't pucker up. However you do it it will be lovely.