I would have to say that I would first pick out my ULTIMATE favorites and keep all of That.
Then I would go back and pick out many fabrics that would go with your favorites and then themes you love ... for me that would be Butterflies or Daisies. I have been collecting them so long. I personally would also keep my vintage pieces. I have very few but love the patterns. Then.. I would compare the piles, try to unload 1/2 and if you can't start with 1/4. Then in a year narrow it down further.