Advice greatly needed for shelving unit this Amateur is building for local business! please!

Hello, I was asked to build a retail shelving unit for a local coffee shop. Heres what i got so far:here and here and two views of the frame of the shelving unithere is how the shelves will fit into the frame. they will all be made of 2x6 poplar joined butt to butt. the middle, waist high shelf will be 4 planks deep, the shin-height shelf as well as three shelves going up the back braces will be 2 planks deep, with a cut-out so that the shelves can sink back into the back braces.the two "spines" of the frame are connected to the internal cross braces with hanger bolts, locking washers and wing nuts so that the whole thing can be disassembled and laid down in the back of a van, in case it ever needed re-locating.Im hitting a wall because I haven't quite figured out how i'm going to attach the higher shelves, while still having the whole unit be (A) sturdy and (B) aesthetically appealing.any ideas?! does anyone know of any appropriate hardware that can be used that im not considering?I know im doing this ass backwards. any kind of advice would be welcomed! via /r/DIY http://ift.tt/2tVM7KN