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.

The small round garden bed within the gravel is the perfect spot for a deciduous tree. You will then get winter sunlight into your home and the tree will block the summer sun. If the area is fairly long, consider 3 trees in a line along the length of the house. In this instance I would choose the same tree throughout. I don't know where you are or what your soil is - this will have a bearing on the choice of tree. But I am a sustainable landscape designer and I use trees all the time for insulating the home the sustainable way. Its remarkable how effective trees are for this. The tree/s can be planted into the gravel, using the gravel as a mulch. Choose a variety with a trunk and a widish crown so that you can walk under the canopy as it gets older. Its a great look.

Sounds fascinating but I can't see any photos yet. Maybe try to post again.

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?