Marble is a beautiful stone. You will need to have it sealed regularly (every 12-18 months and unfortunately if you're a keen cook you should be warned that it can stain and acidic things like lemon juice and vinegar need to be wiped up immediately. I say this as if you're anything like me you tend to share a lot of your cooking with your splashback. The alternative would be to look for a caesarstone type material in a marble pattern - Caesarstone and similar products don't need sealing, aren't porous and are more stain resistant. Good luck.

Try a slim porcelain sheet in a concrete look finish. The large format size means you'll probably need only one, so there'll be no grout lines. Have a look here, at the Portland 3.0. I think the Kerlite range also does a concrete look and is larger, at 3m long. The other advantage of a porcelain tile over actual concrete, is that you just wipe it down. Concrete is porous and will stain.

Your kitchen is small and already quite busy. I would make it as simple and clean as possible. You can't beat ceramic tiles for cost, durability and ease of installation. Have a look at Johnson's Spectrum range to see if you can match the green. https://www.johnsontiles.com.au/product/spectrum/?utm_campaign=1602072422&utm_source=google&utm_medium=cpc&utm_content=304640004469&utm_term=&adgroupid=61761480198&gclid=CjwKCAjw_YPnBRBREiwAIP6TJ0idAicM8vfEevC-WrwRVNmbtUPHfDAjvNpkaOIo0hzN0dwMw9u1rxoC0VkQAvD_BwE You will get a neater finish with ceramic tiles than you will with trying to work with DIY stainless steel, particularly around the edges. There are lots of online resources to show how easy it is to lay smaller ceramic tiles. Leave the large format porcelain tiles to the professionals. Best of luck, Dr Retro of Dr Retro House Calls

I think that it will look too busy with the contrasting cabinetwork and the patterned tile on the floor. But then Australian tastes and styles in kitchens tend to be cleaner and more understated than our American cousins. I would keep it simpler, with a plain large format tile to make cleaning easier and to visually expand the space. Your current tile is very busy and probably hides grease splatters very well. Best of luck with your considerations, Dr Retro of Dr Retro House Calls