The wallpaper in the main portion of the build is drawing paper: Daler-Rowney Dreadnought Grey.
None of the wallpaper is glued in place yet since I have some lighting to work on first, but I tried out the wood ceiling with the new grey paper in place. I liked it well enough to cut the window openings for a more in depth mockup. I love the warmth and visual interest it adds.
Since the bathroom wall will be removable, I'm going to finish the front edge of the dividing wall with 1/2" wide half round trim. This will have the slightest overhang on either side of the 3/8" thick wall and give some stability to the removable wall. It will also mask where the wallpaper ends on that removable wall.