Can respond to a few of your questions. For a totally flat look; photo top before quilting, then again after quilting.
Wool batting gives the highest loft and quilting definition. For a flatter look, use a thin (1/8 inch) cotton batt and no washing before photos.
I do prewash fabric.
When finished, I soak in warm water in the bathtub, squeeze out water into towels, then lay flat, smoothing into shape, on the carpet to dry. In this super dry summer of Sierra Nevada's of California, drying on the carpet is no problem