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.

1. If you are having white tiles on the wall, the same as floor (my preference) then the white bench top will look great. The kick board should be white to match white tiles and the bench will look like it is floating. 2. If you are having 'light' colours, and white basins, then the white bench top. 3. If you go with black benchtop with 'light colour', then I think you need to look at a black basin and keep the kick board black.

Ideally you would want 900-1000mm clear space in front of your vanity and for walkways, unfortunately we don't live in an ideal world and have to work with what we have. 700mm would be the absolute minimum width for a walkway to still allow reasonable passage, although I would be reluctant to go this tight. A floating vanity will help the space look larger and storage can be included in a mirrored shaving cabinet or mirror with shallow shelf above the vanity.

En-suite layout is fine, Looks like you have a double hung window with a slightly lower sill to the vanity height. . I’d put a stool in front next to shower screen. Update vanity and top and splash back, maybe lowering mirror. Could put a niche in the side wall if want extra storage. Could change mirror to a cabinet, even if it protrudes, mine does, A smaller basin would increase spaciousness and bench space. Can also increase depth of vanity, to 550. Replace floor tiles if you want but I’d leave shower if you want to keep costs down. otherwise retile to full wall height will improve look. Could add a pendant light over left side of vanity