I'm not a pro at all, but I am an avid fan of the color gray, white subway tile, farmhouses, and your flooring choice. What about white for the grout? Anything else will highlight the tile pattern, which I think might compete with the floor. I would also use white paint or a very light color in order not to draw attention from the floor. What hardware finish do you have in the rest of the house? You could always use the same finish. If that is undecided, I think brass would look nice with the blue floor tile. Also, if the vanity has not been purchased, what about a wood vanity with a white porcelain top? That would add warmth.

That makes sense to keep the white cabinets consistent. I would make up a few boards with the tile you have chosen using different grout colors (I think white would get too dirty on the floor, but I'd try various shades of gray). Then I would wait until the floor is laid to make a final decision. Then I would post photos, because I want to see this bathroom!

I love the flooring. I would do black grout, just as it is pictured in your photo. I would then paint the walls blue to match the blue in your tiles, or black if you are a little more daring. I don't think the vanity complements the tile. I like the idea of brass fixtures and orb lights.

Don't get that vanity. The floor is the show stopper in that room. Keep the rest of the elements lower key. Get a well made vanity, Even custom isn't that much more in my experience.