I installed marble in a recent main/guest bathroom remodel. But, we're babying it so I can't say for certain how it will hold up to indelicate handling. We use pH neutral soap and marble cleaner and do not bring food in there. I would recommend picking up a sample of marble and either testing it with products you normally spill or at least setting it on your current countertop to see how it holds up to use. I also recently picked up an antique sideboard with a marble top. The marble has a few stains and etches and is quite old (maybe even 100+ years according to the previous owner - but I'm not an antique expert). However, even with the stains, after a quick cleaning, the marble looks fantastic. If you will be bothered by stains and etches and are not careful with your countertop, you may not be happy with the material. However, if you accept that it will possibly stain, scratch, and etch, maybe you will love it anyway.

few ideas for the vanity if staying w/the vintage look. get an actual walnut mcm piece and modify it. Cut off the legs, mount to a stud, cut a hole for plumbing. if you have room, do it like this. best thing is to do a wall mount faucet for your dresser. get a remnant stone piece and have it cut for the sink (that you will fit in a drawer) or, if you're a bit handy, get some Plyboo (bamboo plywood) and make your own counter/vanity. make a mirror frame and shelves while your at it. I've used this plyboo to make my own platform bed/headboard and nightstands. the stuff is great! as for the tile, do a hex of some sort, pennyround, subways, or the 4x4 as mentioned. CleTile.com as some beautiful 4x4 tiles that are reasonable. Fireclaytile.com,,,also great choice,,a bit more expensive. CleTile your shower w/the window is great. could you bring it out another few inches to give you a bit more room? Do away w/that corner seat/shelf. the other option is to put in glass where the wall is between the vanity/shower. you could relocate the plumbing. even if you only got a small portion of glass, it would help lighten up the room some more. check out these cool porcelain tiles for the floor (or the shower). they come in blues/and whites/grays as well as the black. black looks good w/a walnut vanity. do your shower tile in a vertical stack, glazed tile like this: or in the 4x4 or regular subway, like this

Sure, if it looks good with the paint. It would have to be a few shades darker. Since Gray Owl, on the card with the progressively darer shades, looks like it is a greige, the darker colors become brown. So you would have to go to the paint store and find a charcoal that looks good with the greige color. If you go to the Benjamin Moore site (google Benjamin Moore Gray Owl) they will lead you to look at the color in different rooms, and it you go to where you can change the colors for the different elements in the room you will get the chance to see the Gray Owl with other colors. I see it with Silver Spring 2120-50 and it looks great,, a darker gray that will look nice with Carrara. Not Charcoal, but charcoal is awfully dark. This is from that site and it purports to show Gray Owl walls and Silver Spring doors and fireplace. It is worth a look, as the combo looks like it might go nicely with the Carrara. Your veins are quite dark, so might take a darker color. You are there and you can see, we can't, go to the paint store and see what looks good with the marble, take a sample with you to pick out the paint.

The vanity IMO would the 1st thing to go and keep the rest of the finishes simple. So I have no idea how big the space is but if it is a PR why have the shower at all so maybe a bit more info would help. I like floor and shower walls all the same to make spaces feel bigger and I really do not like subway tile in showers since the more grout the more work to keep clean .