Thanks for the feedback. I ordered two more Cedar planks to make two more shelves. I'll post the measurements of the cuts to make it fit snugly. I was going to put a couple of connectors to the planks, but honestly they turned out fitting so securely that I decided against it.

The humidity is slowly going up...it's at 46% today and going up about 2% a day. I'm OK with that because I prefer this technique over wetting/damping the cedar. Of course, when I add the other planks, the humidity will go down some. I'm actually curious about how much it will drop.