I've been quilting a long time. My advice is to buy only for current projects. If you are making a scrappy quilt, then you might need to purchase lots of quarter-yard pieces. If you are making a designed quilt, buy more yardage of each major fabric than you calculate is actually needed; there's nothing worse than getting to the end of a quilt after working on it for a year or two, only to find you need one more yard of something. It is those leftovers that become your scrappy stash.
Quilters have many individual tastes, financial circumstances, storage space, wants, needs and desires. My experience has been that buying fabric can overtake making quilts. I find my large stash cumbersome now, and have spent many hours working on reducing it down to fabrics I might actually want to someday use in a quilt. My tastes have changed over the years so that many of the fabrics I bought 10 or 20 years ago don't appeal to me so much anymore. I would rather spend more money on new fabrics specific to a quilt I want to make than paw through my totes of fabric yet again trying to find things that will go together.
Whether or not you cut up extra fabric before storing it is a matter of personal preference. Leaving it uncut gives you maximum flexibility later on. Cutting it into standard size pieces makes it easy to sit down for 10 minutes at a time, or when you are low on energy, and simply sew for awhile. There are advantages and disadvantages to both, just as there are advantages and disadvantages to ruler-folding stash, sorting and storing by color, etc.
What I have found works best for me is having lots of stacking, clear clamping totes. (It works best to buy a ton at the same time, so they all fit together. Tote styles go out of fashion with unending regularity, which means you end up buying clear clamping totes that don't stack well with the ones you already have.) I don't have hard-and-fast rules about sorting. I separate my batiks into lights, mediums and darks. Specialty fabrics get their own totes -- fabric types such as florals, jungle prints, children's prints, etc. Muslins and solids get their own totes (labelled so I know which muslin is which). Calicos get jumbled together.
If you use totes, be careful not to get them too big. My biggest totes are reserved for packaged battings because they are light in weight but big in volume. Fabrics can make a tote heavy fast, so I have many more medium and small sized totes than large ones. Clear totes are a must for me, so I can see what is in a tote from any angle (including from above). I will only buy clamping totes now, because I found the non-clamping tops tend to warp over time. I quit using permanent labels on the outsides of the totes. Have found it much more flexible to write descriptions on a 3x5 index card and tape it, facing outward, to the *inside* of the tote. This keeps the label from falling off or discoloring, plus I can change the purpose of the tote easily as needed. My favorite stacking, clamping tote has been discontinued. I love those totes because they come in a variety of sizes, all designed to stack firmly on each other. However, here is a link to the type of tote I would probably buy now in different sizes:
http://www.walmart.com/ip/Sterilite-...-of-6/44785810