I know this is probably too late but if you are still looking there are often vintage live edge coffee tables on auction sites that could be upcycled as vanity counters.

I think you are trying to tone with what is there but in a small space I think you need to go as light as possible. I would be looking for a nearly white granite with warmer veining such as artic white (bear in mind they are often called different things by different suppliers) I also like stone type products like Silestone

As above, the sink is supposed to look like that, the same with baths of that fashion. If you fill in the gap that side, it may look odd on the other side. You really need a smaller basin so that the gap around it is larger to enable wipe ups. The other choice would be to have a counter top sink with a back and a small side edge so that they fit in to the corner like this:- It looks like it's next to a piece of MDF, so hopefully it's not fitted yet as that needs painting and sealing otherwise it will soak up the water and swell.

I think you see bars (serving beers) with stools and no overhang. These are fine for a social setting where one person might be sitting with their back to the bar chatting to others in the room. If you intend to use the bar for food you need to face the island so will need the recommended leg room. Could you swap the 600 deep cabinets for 300mm deep? The cost of new carcasses might not be too bad. You should also talk to your kitchen fitter as he may be able to install them after the quartz.