It depends on many things, but also are within these guidelines. A splash back provides a surface which is to be impervious to water, therefore not allow water to absorb, and depending on your state, the regulations directly behind a water point including a tap or outlet is to be minimum 200mm high, and for heat and fire ratings, the area behind a cooktop needs to be 600mm minimum from your bench top is you have an electric cooktop, and 650mm for gas, with the splash back to extend 200mm either side of the heat source either side. So even if you want to only do this, there will need to be quite a bit of splash back, and often people use things like the bench top, window position and overhead cupboards to contain the splash back, providing you a rough idea of where to start and end one. Although not technically required, even in areas without services, a splash back that changes height and doesn't continue around walls to neatly finish off the surface will look out of place, so for consistency, the splash back is best used to effect, and provides an opportunity to incorporate a colour or interesting surface to the kitchen. By no means should a splash back be an after thought or put in simply in response to the minimum regulations. If you have a layout of your kitchen, start where your overhead cupboards are and draw a line around the entire room (even through windows and openings) to see it complete each wall that is part of the kitchen. Meaning any wall that has a bench top attached. Tis is a good place to start. Hope this helps.

Hi Hannah! Wow I love the kitchen! I wish I had seen this earlier so I could suggest but I love the grey tile, it looks like a successful choice! You could add a marble cheese board to the island. The grey streaky tones In the board will probably tie in everything else. You could then put a terrarium on top of the marble board!

Nothing wrong with large tiles for a splashback - though all personal preference, we used them successfully in this renovation with a minimal grout and the awesome texture and pattern of your tiles they will not appear big, I would think they would look more like a mosaic tile. Go with what you love and enjoy!

Hi Sue, I think it would look amazing if you used some tiles with a bit of texture. The wood look tiles that are popular at the moment would be an example. If you chose a colour that toned in with your floor you would get a really nice cohesive look but with a bit of interest. I've attached a photo of a recent design of mine as an example. Just a suggestion!