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,

I agree with Dual Designs that your colour scheme has a potential to look great, and I think dark(er) kitchens are here to stay for a good, good while. Copper adds a warmth and a textured softness of sorts (if metals can be soft, of course, be we are talking comparative feel of the space). I'd probably go for muted kind of navy(ish) or very dark (and also muted) green rather than slate OR black, but a very matte very dark slate might work the best. And yes, pick what will work for you and what you will love, unless you are planning to sell very soon.

I agree, remove that end section altogether if possible. I don’t think you often see a backsplash on the end of a single run.

Nice. I like it.