Lock together to some extent.
In a sense. Imagine rotating it 90 degrees CCW, so the opening is facing up. You'd still be able to lock them together, but if they had handhold slots (which I plan to add), they could conveniently stack together in a closet or cabinet.
Yeah, coming back to this I realize I completely forgot about my original goal of making these lock in side-to-side. In the attached picture I did a quick-and-dirty fix. I think that would work but I'd have to play with it later to make sure. The other nice thing about this is that the shelves would be in contact with each other, lending a bit more strength.
Good thought about the base, I'll have to think about that.
Thus far I'm planning on 30" wide. I plugged the weights into the sagulator and got a good result, but I'll take another look.
That's the idea. I realized I wasn't doing that in the original design, but my revised version is.
This might be a good thing to pair with a base like gee-dub suggested. Once I'm in a more permanent space, make basically just a big thing that looks like an "L" in profile to get a wider base and vertical surface to secure them to. Might be good to make it 60" wide so I could make it 2 shelves wide. I'll probably cross that bridge when I come to it, as long as I plan from the beginning about how to secure them to said vertical surface.