One mirror to the backsplash.

I would do 2, a bigger one over the sink and maybe a makeup mirror over the vanity? Are you a big makeup person? I am putting in an LED backlit mirror for my makeup vanity in my upcoming bathroom renovation...might not look as pretty but it will be put to use!

One long mirror. It'll give you a simple, calm look -- better than a broken up wall, which can get too busy fast.

I think you need matching light fixtures too.

Agree with Mrs. Pete. You need matching fixtures. I'll also add that the fixtures should have globes/shades that diffuse the light. What you have are often very unflattering.

can we see the fixture or a better photo of the entire wall?

I'd prob do one large mirror,,like this,

you have the perfect wall and decor to do something cool in that space. have you thought about doing any tile, ship lap, wallpaper or something?? just seems like a large expanse for that little sink and long vanity.

bringing a nice mirror w/rich wood tones, maybe some cool pendants, would give a little pizzazz

maybe some wood shelving near your make up area (if you don't go w/a solid mirror)