Love your tile! I would wait to decide until everything is in place. I am thinking that once you get a shower curtain added by the tub, and you see the mirror and outlets installed, you won't really have a good spot for a shelf above the toilet. A single piece of art, or perhaps a pretty wall pocket with some greenery in it, might be all you need, and would soften and add color to the space. On the wall to the right, I would think a single piece of framed art, or a stack of a couple of smaller pieces, would be fine.

I have the exact situation over my towel bar/near the door in my master bath. You don't have enough room for 3 pictures no matter how you hang them. I have one larger print slightly smaller than the width of the towel bar centered over the towel bar and 5"-6" above so you have room to hang and remove your towels without disturbing the picture. Something interesting with the colors of your bath accessories?

You can find decorative panels in different sizes and patterns in various places. Etsy, Amazon, Home Depot.... materials will vary. Since you want to hang it consider the weight. In my former home I used a couple of them to screen of an overflow guest sleeping loft that had a pony wall. I lined mine with fabric for sound barrier too.

I would not put anything there. I don't like toilet areas that are dressed up. I would paint the window if possible. If you need privacy you can get static cling window film. There are plain and lots of colorful choices available. https://www.homedepot.com/p/Brewster-47-in-x-24-in-Dogwood-Premium-Window-Film-PF0700/300573711