I think it would be best if you could attach a photo of the space.

Can’t see why wall up the stairs will look odd empty with one/or two, but without seeing the wall it’s hard to know. Just test using peelable two sided tape. My priority would be ensuring their sizes feel right and are related in some way vs the empty staircase wall.

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.

@tracefloyd Thank you. On the handrail side is just air. It's open. no wall there.

I'd do a gallery wall but perhaps also hire an electrician to put in some better lighting for you.

Some examples:

Transitional Kitchen and First Floor Leesburg Remodel - Naperville · More Info

Modern Farmhouse Full Remodel - Addition · More Info

Top or bottom. This is a narrow staircase and I think not the best for a gallery wall.

I would put art on the wall shown, on the side with the light switch. Skip the wall with the bench, then continue the artwork up the staircase if you have space.

Thank you @ilikefriday