Mmmm More to consider!
The hive is 21" deep Ive built it with 3" thick walls, 1/2" plywood, 1 3/4" insulation and 3/4" T&G. The bottom is also insulated.
The frames are a bit longer at 19" and reach down to 1/2" above the mesh floor I've made some frames with just a short 3" starter strip...