I'm coming late to this party, but it is a good one!
In terms of materials, I've made DIY Symposium shelves before which are CLD. Any logic in making these out of an aluminum/HDF (ie harboard)/aluminum sandwich? It might make it cheaper than straight aluminum and would it not make for a less reasonant frame? I appreciate it would be 3 times the CNC work, but I thought programming the CNC machine was the really big cost?