Your best bet might be to cut out 36x72 cardboard and test. Try centering within the 96 inches, but also try lower.

I the mirror sounds very cool.
But, I think I’d just go with a massive piece of art.
Or a big family photo.
Or just wallpaper.

Personally, a mirror there wouldn’t work for me. I don’t think it will reflect anything important. Or worth seeing twice. Lol.

It’s difficult to suggest something for the stairway wall without knowing the decor of the adjoining spaces. Can you post more photos?

I'd select something that cascades down the wall —nothing as static as a mirror.

IMO we need to see the whole staircase and get some clue as to your style. I agree no mirro and that one shown is good example of why you do not do it,

If a mirror doesn't reflect something interesting I discourage it's use. In your case I would opt for an extra large piece of artwork - something grand in scale.

This is very helpful! Thank you so much!

Ooh, I love those green bowls that BeverlyFLADesigner suggested. I like the fluid organic design they make

Feels like clutter to me reminiscent of the days we got baskets at Pier One to fill dead space : ). Three of something strongly related/stepped up, is not really the same as "gallery"

24 X 36......with 4 inches between them equals 80" total "width" on a wall 103 inches wide

Pick the starting point nearer the foot.

https://www.greatbigcanvas.com/view/feather-ii,2049521/?ref=also-in-similar-image