If you want the wall and floor tiles to be the hero in your bathroom I recommend you keep the vanity very simple. The white cabinet you have will be least obtrusive with a 'white' top. I love the elegance of stone and man-made stone is generally more durable. Check out Caesarstone Organic White or Frosty Carina. Although Frosty Carina has more pattern than Organic White, it's quite discrete so shouldn't compete with pattern on the tiles. If the tiles are charcoal or a dark brown/grey then either should work. Love to see a photograph when it's finished, whatever you decide.

we think you mean 1800 mm wide (left to right) and 460 mm deep (ie front to back?) why not make a newspaper paper cut out for the sizes you're considering and then add different size and shaped basins to see how it feels ...one important point to consider is not only would a deeper basin have more counter space which is usually good, it will also use up floor space which can make a HUGE difference for opening doors and architraves around doorways and for shower entry and standing and walking room so check the size and shape of the room first and then see how everything fits together although i'm hoping that if you are aiming for an 1800mm wide vanity that the room will be quite generous...btw if you like curves you may like to consider having a vanity cabinet made with curved edges as well as adding a curved sink

Is your final photo of the vanity you already have? I also thought adding legs would take it back to the MCM you are after. Would be interesting to know how the silver drawer pull is attached. Not sure about painting it matte black as I thought timber furnishings were more prevalent then, but it's totally your choice. I hope you will post updates as you go. I just love mid-century.

a separate wiw and ens will give the best use of the space with maximum storage wall to disguise the volume of your clothes in chests of drawers under hanging space below high shelves and there's space in the ensuite for a generous double shower, vanity and wall cabinets but the bath will have to go elsewhere if you want to be able to stand and dress in the wiw or ens and keep the rooms feeling comfortable for two people to use together twin highlight windows will provide light and ventilation and hinged doors allow for clothes racks and/or hooks on the back of the doors