I think this room already has a beautiful classic foundation, so I’d keep the updates simple and balanced rather than filling every empty wall.
For the 11-ft wall, I’d choose one larger statement piece around 60–72 inches wide. It will feel more intentional and less busy than several small pieces. If you prefer a gallery look, three coordinated vertical pieces around 20 × 28 inches each would also work well.
For the areas beside the windows, I’d keep things lighter — a pair of narrow botanical prints or tall greenery would add balance without competing with the windows.
I wouldn’t add too much around the mirror either. A pair of small sconces or narrow framed pieces is enough; leaving some negative space will make the room feel more elegant.
Since you already have white glazed cabinetry and Calacatta marble, I’d use antique brass/warm gold, medium natural wood, or a very thin black frame. Artwork with warm neutrals, muted blue-gray, soft olive, taupe, and touches of brown would tie everything together beautifully.
I created a quick visualization to show how these ideas could work in your space. Hope this helps! 😊
Q