What are the benchtops going to be?

A cheaper alternative to glass is the metaline range from Laminex, and maybe something to consider Laminex launched this product to compete with glass splash-backs. Your cabinetmaker can install it, and it can be cut on site as required to fit around power points etc. The range of colours are obviously limited compared to a paint finish but there are some lovely metallic's in the range - I'e added a photo of our sample folder to give you some ideas. In regards to the colour itself, you could stay with a neutral, but I would go for a splash of colour! as the rest of the kitchen is neutral, choose something that you just love, and will work with your planned decor, and go for it! I would think about putting something on the back of the island bench as well, timber is being used beautifully these days, so depending on your floor tiles it could add a lovely warm touch to your area.

I would go for high gloss black tiles. I know you said natural light is low but you can get black tiles with such a high gloss they reflect a lot of light. The black would look dramatic.

The benchtop in the kitchen is the hero piece. Go neutral so you don't draw attention away from the benchtop into the butlers pantry. The splashback is usually well hidden in a butlers pantry by things on the benchtop. You have enough happening already without adding yet another feature. Best of luck, Dr Retro of Dr Retro House Calls