I started with fat quarters.....now I tend to buy a minimum of a whole yard. But I like quilts with a lot of different fabrics (at least 6-8)....so 1 yard works. If you like quilts with a fewer amount of fabrics, I would get 2-4 yards.
I try to only buy for my stash when fabrics are deeply discounted/on sale. I tend to gravitate to certain designs/colors so that helps!
I have bought 3-5 yards of whites/neutrals and black when I have found them on sale.
I just can't afford to buy 4-8 yards at a time....unless it is something I am buying specifically for batting.
But my stash is small compared to some and too large for others.