I would only do the back to the window sill but if you have to do the side, then don't go past the bench top. Depending on you tile, end at the edge or shorter.

I think it looks fabulous as is, BUT I know what it's like to have something in your mind and so anything else falls short. You asked for that and I gather they said they could do it, and then in the end they haven't, so you're not being unreasonable to ask that they re-do it according to what you had agreed on. I do think it looks great, though I suspect every time you look at it (many times a day!), it will bother you each and every time! And any discount you've had won't diminish that daily reminder! ; D We had our timber floors sanded and varnished and the tradesman (who was recommended) sub-contracted the job to some very shoddy flooring guys. The job they did was terrible, the tradesman was apologetic when he saw them and offered to not charge us at all (which my husband was tempted by!), but thank goodness I realised that I was going to have to live with those floors and I simply wanted them to look great so they came back, re-did them and we still paid full price. There's the odd area that's not great that bothers me, but I'm so glad I pushed to have it done to the standard I expected. You may experience the same?! Good luck!

Tiles are always good, either small textured tiles, or large format tiles (less grout makes for easier cleaning) it really depends on what kind of style you are going for in your home. Is it earthy/rustic or glossy/contemporary. Or mid century.... too many choices.

Agree with others. I have had black shiny glass splashbacks and that was an absolute nightmare to keep clean and shiny. Definitely matte, and careful with the tone of grey as some lean toward blue or yellow so you want to match the grey in your beautiful benchtops. Hope this helps.