This is my proposed design for your tiny WIC. The concept is clean so I put the material, form, and shape as clean as possible. The Layout is L shaped and utilizing all the space, so I made the closet full up to the ceiling. You can still access the furnace room, I made an access door with mirror in it and wooden frame so it looks like merges with the closets. Beside the furnace, the wall with the door to this room, I made shoe rack along the wall.
All of the closet is designed with door except for the hanging clothes, so the room is still look nice, neat, well organized. Along the top of the closet I made cabinets to storing bigger things. In section A, beside the hanging clothes, there is a closed cabinet (sliding door) for you to storing folded clothes, and some drawers to storing maybe some accessories, shocks, ties, etc.
The material I choose is combination between light wooden (plywood+wooden laminate), white painted closet, and frosted glass for the doors of the cabinet. Please consider my design and I hope my design will help you. FYI, my drawing for plan and section is use centimeters unit.