Some removable options; cover mirrors with removable wallpaper, or use liquid starch & fabric and apply like wallpaper. Or install a track I front with panel curtains. Just means for access you'd have to slide those across, then the wardrobe doors. If you're not worried about it damaging mirrors, stick paintable wallpaper on or wood panels. Or just simply paint.

You could fit it out with narrow shelving unit that is flush with the doors, ie. rest sits inside wardrobe. So has that build-in look. Light the shelving for display pieces, or not. Use to house a sound system. Some shelving units come with a glass door which would be good for display items. Or fit shelving with a push hinge door and use as additional hidden storage. Or as a shoe cabinet. Or do a series of small floating shelves that come out into the room if that's practical. You can get some with pull out draws. Otherwise, mount a LED light panel or backlit wall panel art?

I guess regardless of whether it is a single 1800 (4 door) or 2 x 900mm (2 door) the issue of the doors banging is an issue. but the 2 sinks are at one end so i can't ever imagine doors banging will be an issue really. my main concern is whether 600mm is too big for a single door (and the need to step back out of the way when opening the door)

It would not look odd and is quite common. I've sold many robes over the years that had shaker-profiled sliding doors. I would highly recommend a heavy duty track like the "Indaux" system Nover sells and use 18mm doors.