We are trying to think like the installer. We realized that our machines will have to be connected, leveled, and then pushed into a very tight space. So, we decided to: 1) max on insulation in floor and adjacent walls to try reduce vibration noise. 2) plumb the back and side walls according to where the machine outlets are (water, electricity, dryer vent). (Got a diagram of the back of the machines from the owner's manual) 3) install a Watts IntelliFlow (about $200) for leak detection 4) stub out the waste pipe already there for a pan because a delivery guy we consulted told us that they may not be willing to lift heavy machines over a lip, so we abandoned a built in, tiled pan. We would have liked to have a real floor drain but code requirements made this another $2000 worth of plumbing. 5) bought braided, steel hoses for extra measure. Here is a link that might be useful: Watts Intelliflow

I think it would depend on the width of your door. I'd go for the deeper shelves if the door is very wide. E.g., we have 66" wide closet that we're using as a pantry right now, but it has double doors that extend almost the entire width (two 30" doors). Because we don't need to worry about "reach in" room, we have deep shelves. If your door is fairly narrow, though, I suspect the shallower shelves would work better.

!2 inches is what you have in your kitchen upper cabinets.. Go try that. Empty a cupboard and fold Now what do you think? I'd want 18 inches, You will too. That's why dressers are 20 inches deep overall. Ignore this advice if you are Marie Kondo and your screen name is an alias. !2 inches are SHOE /handbag shelves and not much more than that

You can hang clothes the other way round, using a pull-out hanging rail that is fixed to the underside of a shelf. This is an example, just so you know what I am talking about but I cannot vouch for the quality. The shelf would need to be able to support the weight of what is on it, plus what is hanging from it. I tend to agree that building and installing shelves would probably be best. If that is not practical, or if you are not sure if the walls will support shelves, the IKEA Billy range is 11'' deep, so might fit inside the closet.