I'd hang 2 pieces of art side by side on the long wall.

What exactly are the plans to enclose the pipes? Seems like a very small cabinet unless you plan on making a closet along the back wall.

It is going to be pretty small, The actual dimensions of the room are 4'x8'. The closet is going to be about 10" wide (what you will see from the doorway) and 24" long. It has to be able to completely open, so it will need to swing out toward the back wall. I had thought about putting floating shelves on the back wall, but can't do that now because the cabinet needs to open.

Looks like there isn't a lot of room for anything 3-D.

I'd probably put glass shelves on the small wall and some cool decal artwork for the large wall.

This is a DIY which would look great in your bathroom

Or decals:

Would doing something like this work? Or would the chair rail with the pallet wall look strange?