Thats a really tight and narrow space, For that reason I would consider wallpapering. Anything with any depth will impede on the already limited space. Mirrors facing mirrors is a no. If you can find large art that has shallow frames that would work.

I would do a wall gallery of art. I would rather have art reflected in the mirror instead of patterned wallpaper

This idea:

Wainscoting on all the walls. (Check out Home Depot, Lowe's for easy install wainscoting.) You can keep the vanity the color it is, as long as you find a big piece of art which will reflect in the mirrors. Go dark with the art, but include the color of the vanity in it.

Hard to match a color on a monitor, but possibly B.M. 626 could be a lighter green than the vanity. And it likes black.

You have different finishes. Keep the black as faucets can be expensive to switch out.

The cab over the toilet? Gone!

I think wall paperwould be awesome . I would not add more mirrors refelections are a bit weird when you have mirrors facing eachother. To keep that space from feeling even more tight look for maybe a mural type wallpaper so it looks like looking out on a scene.sort of like this the bottom one pretty moody but nice

Add a few recessed downlights in the ceiling and select a light background wallpaper for the walls. It will really make a difference.