One of the first principles that I discovered around organization was the 3-9 principle. That is as you get to about 3 things that need to be organized you need to think about ways to group them. Any more than about 6 items need to be categorized further with about 6 items in any given category being about optimum. You need to have an additional organization method for any more than about 9 items.
There are lots of reasons to have more than 9 items in a category, but keep it simple. This principle applies to items of the same thing.