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.

first decide how much counter is needed and if you prefer surface mounted or drop in sink...we chose the smallest drop in sink because it allows for generous counter space and because they're so comfortable to use they looks perfect

Thanks everyone! Incredibly helpful advice!! And the photos really help me to visualise the space - so that is super helpful. I'd love to have more storage behind mirrors but our wall has too many braces, and framing so can't do recessed storage unfortunately. Might be able to do storage that isn't recessed (behind mirror). I'd need to look at the measurements. Thanks again!

as a buyer i would be looking for a spacious uncluttered looking ensuite not twin basins squeezed into a small vanity..imo the counter isn't for storage itá place to rest a glass, dryer, toothbrush or stand toiletries until they can be put away in the wall cabinet but there are so many different vanities and your favourite will be différent to others and it's quite easy to replace a vanity as long as there is enough available space...i would choose a wall hung 1200 wide vanity with a single drop in sink and only consider twin small drop in sinks with a minimum of 1500