I have one, I started at the bottom and worked my way to the top. I used identical frames, in varying sizes. I think it tends to gets busy/messy looking if you either don't match the frames or if art is mix and match in theme. Mine are all family photos in black and white, starting with wedding photos and working up the stairs is the progression of our family with newborn and 1-year pictures of baby 1, 2 and then 3. They are now 13, 12 and 8 so I love admiring their baby pics every time I go up the stairs. I will say, in a high traffic, narrow staircase, be prepared for them to get knocked around here and there. Especially if you'll be going up and down with a laundry basket, etc. Be sure to use good hardware for hanging. It looks like a newly painted stairway (what color? Love it!) so definitely take the time to use paper and cut to size and tape it up as a mock gallery, with painters tape before lifting a hammer. The last thing you want is holes and spackling after you decide the layout you chose wasn't measured right or looks too busy with the spindals. etc.

Also, if it's a new build, wait until all upstairs furniture is delivered and in place before you start this project. Movers are NOT the most gentle to your walls!

In your space I think a few larger prints in larger format will look better than many smaller ones. It's a narrow staircase and you don't want to detract from your beautiful railing and woodwork.