I don't prewash fabrics. I do test anything I suspect might not be colorfast by placing in water to see if it bleeds, then rubbing against a white fabric to make sure the dye doesn't crock.
As long as there is a reasonable amount of quilting, there should be no problem with distortions due to shrinking. I like an old-fashioned crinkled look to my quilts anyway, so I use (unwashed) 100% cotton as the batting. Everything shrinks together to create that soft, antique look.
I always wash my quilt with Synthrapol the first time in case something bleeds. Synthrapol suspends unset dye particles in water so they rinse away instead of settling into other fabrics. Synthrapol is widely available in quilt shops and online; Amazon has it now.