I have a double right now (one large, one small) and I use the small one to drip dry anything that doesn't go in the dishwasher. It's convenient, but even so I'm planning to switch to a single large sink in the future. I haven't found any double sinks that I really like, but I will admit I haven't seen a great solution to drip drying pots and pans. I really do use that second sink a lot (even if I towel dry my pots, which I don't usually bother to do, I still have to have a place to put them until I've finished the dishes). Most dishracks I've seen are intended for plates and utensils, which I just put in the dishwasher. If I can find a good dishrack for pots and pans, then I will be very happy with a large single basin sink I think.

I only specify an overmount sink for clients if the benchtop surface warrants one. The last time I did was because the client wanted a timber benchtop. I managed to find a beautiful black quartz composite sink that worked well and looked like a feature in the kitchen because it matched the colour of the cabinets. My usual go to sink is definitely undermount because of its aesthetic and practical advantages. Small chips can always be smoothed out if need be but really, there is no substitute for being careful!

Our neighbours are not experiencing the same issue. I'll ask the plumber whether he replaced our old supply pipes. I assumed they did as we took away some copper piping for recycling, but maybe there should have been more. We did not have this issue prior to our renovation and we have been living here for about 25 years. The house is on mostly clay soil. The red slime is on the grout AND the tile itself. It is also on the rim of our brand new washing machine.. I can't see it in the laundry tub or kitchen sink, being stainless steel. I am collecting water from the kitchen tap in a plastic container to see if I can replicate the bacteria there (I hope I'm NOT successful in that endeavour). The bacteria seems to be where the water is in contact with the tile and also around the bathroom sink hole where different soap is used. It scrubs away easy enough with no residual staining on the tile or grout. BUT it keeps coming back.

I would attach it to the vanity, it is awkward to try and reach behind you if you attach it to the wall or you could try a freestanding one that you could put anywhere though they might take up a bit of room when space is a bit tight