I like the look of a simple backsplash using the countertop material rather than using a mosaic there. We used a 6" tall splash instead of 4". We just finished our master bath last fall and we used the Emser Lucente Lazzaro for one shower wall and the niches. Lazzaro has a lot of light greenish-gray-marble colors in it. Lucente comes in a lot of colors. My local showroom only had 2 colors on display, but the Emser website shows a lot more options. If you use Lucente I have one suggestion regarding installation. I don't know if this will occur with a different color, but with the Lazzaro color, there were some marble pieces that had black dots in them. That was fine as long as these dots occurred randomly, but it just so happened that some of them lined up in one area when being installed. The installer was so close to it that he didn't realize. His helper was standing further back and noticed. While things were still wet, he cut out the offending pieces with a utility knife and replaced them with a piece from another sheet. Just an installation detail I thought I'd mention. Our colors were: Emser Uptown Sugar Hill for field tile in 12 x 24" (it's a light gray/concrete color with some variation), Lucente Lazzaro linear mosaic for one wall and niches, QDI The Rock 3" x 3" floor tile (charcoal gray), marble countertop and tub surround with marble splashes, white vanity cabinet and tub skirt panels, a large linen cabinet stained in a medium brown tone and some floating shelves also stained, and existing wood floors. We thought a white and gray color plan might be too cold so we incorporated the greenish-gray mosaic and the stained cabinet, plus a teak bench in shower to bring in some warm elements.

Looks like your sconces might be positioned a bit high

Take a look at the tiles in the pictures below. For a traditional home, the top 2 of your photos look too modern. (try changing the hardware on vanity to a finish that coordinates with others you already have. Can't tell exact finishes from your photos but I would not use chrome - keep it to maybe a satin or brushed nickel or antique brass. One larger mirror in a wood frame to match vanity would open up the space. If possible, turn the lights to point down instead of up. or place one (lower) on either side of wood framed mirror.

In kids bathroom, will I regret not having tile all the way up the wall over the vanity?