I ALWAYS prewash all of my fabric with warm water and dry as I do all of our clothes. I don't like how dry my hands get when handling the fabric if I don't prewash.
IF I SUSPECT A FABRIC WILL BLEED (9 yards of gorgeous green batik), I now use Retayne with that fabric when I prewash. After 6 washings and 7 color catchers (first 6 turned green), I learned to love RETAYNE. It holds the color in the fabric and doesn't allow it to bleed. When this quilt is completed, I will wash with Syntrapol (this does not allow any dyes that are floating in the wash water to adhere onto the quilt).
When quilt is finished, I throw it in my HE front loader with Tide sensitive detergent (my usual detergent), wash on cold and then line dry outside on the clothesline. Others will not be as careful with the quilt as you are because YOU are the one who put all of the work into that quilt.