If you ever expect this quilt to be washed, wash the fabrics before cutting them!
Some fabrics have VERY BAD manners. They bleed, they shrink, they won't unrumple even with pressing, they ravel badly, they change shape.
Avoid unpleasant surprises.
I've started to soak my fabrics in a bucket or basin of HOT water for a while (at least half an hour) before washing GENTLY in warm water.
I keep the colors separate at this stage to see what they do. Just discovered a green I bought recently is spilling - the same green print I had bought earlier seemed to be okay. Now I need to find it again to recheck it before I go any further with that project.
The spray sizing is helpful - especially if working with bias pieces.
Some fabrics don't spill a bit of color - some pieces just won't stop spilling color - they might as well be discarded. Why risk ruining a whole quilt to save a few dollars?
An example of why prewashing/preshrinking is a good idea: I acquired a cute skirt that had appliques on them - when washed, the appliques shrunk and the adorable skirt is now only okay. The new owner said she wrestled the appliques into better behavior with an iron.