I am doing white carrera on my island, soapstone on the counters, white wood cabinets,Restoration Hardware silver sage on walls, oak floors. 1. My original plan was to do a smoky gray/green matte glass backsplash. Will that be too many colors?

2. The painted wall areas will be very minimal and not near the stove or sink-do I still need to do an eggshell or semi-gloss paint or can I do a matte paint? My daughters are teenage, neat girls-not small children!