I think your tiles need to be larger. Choose an interesting, but simple pattern similar to the one below. I also like the idea of something that is from the region you live. Without seeing your space it is hard to know. You say a stone fireplace, what kind of stone? You want the tiles to go, but to make the fireplace stand out do not go too matchy. Mixing concrete with the tiles can create interest, too.

Tile paint! Some people love White Knight's range. Personally, I am amazed they would be durable enough to walk on. But others here may have had first-hand experience...

I have a courtyard that I had a quote from Stratco to enclose into a room. They were going to use wall panels with windows and a sliding door. I ditched the project when I realised the costs were enormous as I'd have to excavate and repour the concrete and move some plumbing as well as look at heating/cooling options if I wanted to use it all year round.

On first impression It seems the design is inherently working against your desire to have the 2 spaces to "feel separate"; from the screenshot it looks like the kitchen bench design (same modules, colour etc) and the open shelving do not help by making the splash back of the 2 spaces "continuous". Rather than thinking just about different materials and colours - perhaps rearrange the storage/cupboard space to create more visual separation? For example: having some full height cabinets against that dividing wall and have the outdoor kitchen a different design altogether?