I really like the look and the dark wall! Love the black wall - make it an accent wall? Hardwood floors with rugs for master bedroom. This is what my bedroom will look like when we move! But with blue walls and a black wall.
I don't think I would use black shower curtains to make a room look larger, but the idea is a good one. Maybe curtains the same color as the tile, or a loghter shade of taupe. Floor-to-ceiling shower curtains. Make a small bathroom feel more luxurious.