i think i have a rather large stash. i've never counted but i would say its over 1000 yards.
i store my stash in closet in my studio and i also have a bookshelf of fabric.
i sort it
1) if for a specific project - they all get stored together
2) if from the same line - they all get stored together
3) if from the same theme - they all get store together (japanese, batik)
the amount of fabric you buy really depends on the type of quilter you are and what you plan to do with the fabric.
i have a stack of japanese FQs and a stack of fossil fern FQs both for specific patterns - otherwise i never buy FQs because 1 FQ just isn't enough fabric for me - i'd rather have a half yard which is 2 FQs.
if its a novelty print i'll buy anywhere from 1/2 - 2 yards depending on how much i love it and how i think i'll use it.
if its a blender, tone on tone, solid batik, gradations, ombre or large scale print i'll buy 2 - 4 yards depending on how much i love it.
then i buy PFD by the bolt - i don't consider this part of a stash since its just white fabric waiting for me to paint or dye to turn it into something i can work with.