Every manufacturer that I know of in the U.S. makes a metal piece to cover the space in the back of a true slide in range. If you are having new countertops installed, then you would have a piece of countertop cut for behind a slide in range and install a support piece for it to sit on (2x4 nailed onto the wall). Then it looks continuous around it. I have never seen a true slide in range that didn't have a lip on each side and the back that is supposed to sit on top of the surrounding counters and close up any gaps. Makes me wonder if the cabinets or countertops in this kitchen were raised for some reason so that they are higher than the range. Ranges have adjustable legs, but they can only adjust so far.

What colour should I paint walls and what colour tiles would go well with all above

I'm changing my kitchen worktop to a pale grey with white cabinets and I was going to have my island in a white worktop with grey cabinet underneath would this be ok ?

I'm currently getting quotes for quartz worktops, how much roughly should a m2 cost ?