Yesterday I felt like I was playing Jenga in a clients storage space. There are about 4 different types of bins, a multitude of boxes, and lots of random bags. In the end everything fit but it wasn't pretty. I feel more space could have been made if the storage containers were uniform.
Its totally understandable about trying to utilize what you have when getting organized vs buying alot of supplies. It comes down to evaluating how much space you need and what aesthetic you want. I am a big fan of trying to use what my clients have already. Spend money on what matters. But on the other hand, if space is to be made, bite the bullet.
Using stackable bins when organizing small spaces is a must. Areas that need stackables include linen closets and under the sink.
Also, I am not a fan of storing items in cardboard boxes. They don't protect your items from elements. They also lose their shape after years and get crush when stack upon one another.
If you are putting the items on built in shelves in a storage area or pantry, then the stackability doesn't matter as much.