I can tell how I maintain my stash;
each time I buy yardage for a project I round up all requirements, exam: anything requireing 1/2yd or more, I purchase 1yd,
I purchase fabrics on sale, lots of neutrals, off whites 2 to 3 yds. Multiple colors that I may use for borders, I purchase 3 yds, backings anywhere from 5 to 8 or 9 yards. Fat quarters on sale, esp if I have something in mind for down the road I stock up on FQ, remembering to get lights, mediums, and darks.
Hope this helps you to get started. enjoy the process