firstly , Are you sure that the cooper tile can not be cut around your sockets ? i'm sure it can be possible to be done , it does take time ,precision,patients and a professional with the right tools to do it, they are called Tile fitters, secondly, choosing a cooper veneer is actually a brilliant idea,comes in many colours designs and materials and cheap to create (it is somethings i can supply and fit.) it would be good idea to glue the veneer on to a mdf board and then measure, cut then install, the right trade people to do or can do are called kitchen fitters or a carpenters,

https://www.splashbacksuk.com/printcopper.html?height=750&width=600&gclid=Cj0KCQiAh9njBRCYARIsALJhQkFFrO6l9_qv0A6bd8cq36MMOEjHc_9NE0Kd0iqpIbMhgvrR9H4FxYUaAjvJEALw_wcB https://www.custom-splashbacks.co.uk/splashback-colour-samples/copper-aluminium-composite-splashback-sample/?gclid=Cj0KCQiAh9njBRCYARIsALJhQkEcPfobm3p_jze1wlvMvOs2igChGod4bWVk1W7hgZSOz2k4lg9vRskaAu4SEALw_wcB

I think I’d personally stick with something neutral then use the bright colours elsewhere. You could always paint the wall above the upstand in whichever colour you wish then protect with decorators varnish so it’s easy to wipe clean. For the cooker splashback you could use the same quartz as the worktop and upstands for a seamless look. Or... I think a sheet metal would look fab and fit in with the industrial aesthetic, something like a brushed or galvanized steel or an aged zinc. No idea on prices but this site does sheet metal: https://www.metalsheets.co.uk/kitchen-backsplashes/

I don't have a Quartz worktop but i think you need to go along to the stone supplier and choose it firsthand as they can vary and it looks a lot different on a big slab. I don't know if your kitchen supplier is supplying the worktop or if you're sourcing separately? If you can I'd choose someone local if possible to cut down on installation costs. Make sure you take along the unit and floor samples too. I know lagoon is a very popular choice and I came across this a while back although appreciate it's a few years old so I'm sure there are others on the market. The kitchen sounds fab btw :) https://www.humphreymunson.co.uk/6-alternatives-to-carrara-marble-worktops/