I spray painted them and then used zip ties to hold them together. It served as a cube organizer for my daughter until she moved out. I did 3 wide x 3 high with a board on the top to place items. It was a great center for her stuff. You could add bins to them as well.
Here are some ideas for you: https://www.youtube.com/watch?v=G-TDp4C3N3I
Hi there, here's a cute idea if you need extra seating. https://www.hometalk.com/5242925/comfy-stools-made-from-old-plastic-milk-crates
Milk crates can be used for so many things. Here's a few good specific ideas though https://fluxdecor.com/diy-ideas-with-milk-crates-or-wooden-crates/