Your palette and materials look lovely - I imagine you are excited to see the project come together. For the vanity, given your neutral and serene palette, I would suggest one of 3 options: white, grey, or wood stain. There are lots of variations on baths with that color scheme. If you do choose a wood vanity, I would try and repeat that finish somewhere else - whether it is wood floating shelves, antique armoire or wood top at a makeup area - all of which could be options for the "nook" area. Good luck.

About the extra space you have in the room- first do you have storage/linen closet in your new room? If not, this may be the space for it. What are you currently using for your hair/makeup area? If you do use it for a makeup area, I would use the same countertop material and in the sink area. I would do a mirror that goes from the ceiling to the countertop and wall to wall for a nice impact. How would you feel about adding a very dark brown almost black wood vanity/shelves for that area?