Laurie I had the same concerns. I saw a number of vanities from NY vanity in a showroom and was not impressed. No dovetail joints and the sliders for the drawers are on the side so you see the rails when the drawers are pulled out. They don’t slide or close smoothly. I just ordered our vanity from Yorktowne (same as Medallion).

Since the vanity is between two walls, I'd purchase a cabinet with appropriate filler to fill the entire space, then have a counter templated. I wouldn't want the vanity floating in the hole between walls. Build it in, like the current one is. You can still have open shelving or legs on the bottom if that's what you like.

That sink has the counter all in one You get a piece of stone cut to fit I do it all the time or just keep the all in one . The vanity can handle any stone you choose .

I would have a mirror madeso it goes all the way to the ceiling, mirror is fairly inexpensive and it will make the room look much bigger, perhaps do one with a bevel. Or if youre buying a framed one u probably are needing a size of 72x48 minimum (that will put it almost to the ceiling and look great :-) Ds