I'm in the middle of a closet renovation also. If you want to do hanging shelves, you should beef up the back wall while you have the chance. I'd make that middle unit with the top, bottom and one of the middle shelves permanent and then put holes in to make the others adjustable. Use a 1/2" back to tie it to the wall.
Go look at the ClosetMaid site and look at the dimensions of their products and the assembly instructions. You can reap a wealth of closet knowledge from there. I basically used the assembly instructions to figure out the parts I was going to need and what I was going to modify.
I made my units similar to their Space Creations Premier units, but did them in 3/4" cherry plywood rather than particle board and laminate. The trim is all solid cherry. With the exception of that darker top rail, I routed and made all the face frame myself.
The 14" depth is perfect for closets. I would strongly advise sticking with that for closet shelves and boxes.
I looked at hang rods at several stores and ended up ordering the ClosetMaid nickel plated rods. They have really nice hardware and come in a variety of sizes.
I did mine as modular units, so I didn't have to hang anything, it all stands on it's own.
I would strongly recommend spending a few extra dollars and get the Woodpecker shelf hole jig, and use a plunge router with a up spiral bit. You will get excellent pin holes that way.
Here's a few photos, it's hard to get a good view from inside the closet.
Next step is three 8" drawers and two 6" drawers to go in that unit in the bottom photo.
Holler if you have any closet questions!