This is one of those situations where wallpaper would cover the starkness of the wall and add some color at the same time. It's cheaper than buying new furniture and leaves the space open to walk freely. (You can also add a curved bench if it still seems naked to you)

Please submit more photos of the room taken gradually going all around. I can say a few things for sure, Having the sectional and the chairs all against the wall is breaking one of the commandments of furniture arrangement. It is not good at all. If the mirror is to stay, and I am not convinced yet, the seating has to be arranged first, the mirror should be hung vertically with some interesting things to the left. Hanging it horizontally like that makes it look like it belongs over a bedroom dresser. And really, I would rather see it hung vertically over a dining room buffet towards the left so it reflects your well-dressed table and chic diners, and to the and you can hang some vintage plates and bracket with an urn or marvelous candlesticks, etc. Your problem with how to arrange the furniture is why so many Houzzers despise sectionals. When one moves, they just don't work, and they don't play well with other furniture. Are you staying in this house? Have you thought about getting rid of the sectional and purchasing a good quality clean-lined sofa such as a tuxedo that you can have forever that will go with everything and fit everywhere? I haven't seen the rest of the space, but the chandelier seems excessive. On the other hand, the rug is underwhelming and boring. You packed a punch with those strong blue chairs and wall. But the rug is blah. Why not get an Oriental or Persian carpet? The coffee table is underwhelming. Why not get a large ottoman and you can put a large tray on it? You also need a smaller table for the two chairs.

They are super helpful is you have an open staircase to a basement. If you heat with a wood burning stove in the basement. We love ours. The light fixture can be four or two bulbs and it has a night light type glow above that. The fan is reversible which is very handy.

I agree this is not the best wall for an ascending gallery. You don't show the handrail wall but you could possibly have a pair of pictures facing each other at the bottom landing...one on the handrail wall and one on the light switch wall. Then at the top, something that creates a cozy space for the window seat...a pair of opposing pictures facing each other on each wall to the sides of the bench, similar to the downstairs arrangement. It would be pleasant if the four pictures -2 up and 2 down- had the same theme or style, even a set of 4 matched frames/art. Kinda unite the upstairs and downstairs.