I used 3/4" Pine for this project because it’s what I had laying around. I would recommend whatever your wood choice is, that it should be at least 3/4" thick so that the bits seat properly and there’s enough meat on the bottom.
I also used a 1/8" 2-flute straight endmill. I like these bits because they have a very long DOC and they also leave a cleaner top edge with less cleanup required.
This can be as intricate as you like. Sand, stain if you prefer, or leave it.
Enjoy your new bit caddy!