There is no specific regulation but it would not be recommended behind a gas cook top. If there is a concern you could install the timber behind a glass splash back for protection. There is also a really nice tile that looks exactly like timber as another option.

I think that would look great with floorboards in a classic walnut colour, that would definitely look great with the light cabinets. If you want an idea of how it might look with the end finishes, you can type this into google and they should be able to show you a few.

Have you priced having the whole lot re waterproofed and tiled? You are already doing the hardest section, it may not be that much more to do the lot. Otherwise agree with above match to the white tiles in the rest of the bathroom. But it will always look like a repair.

We have what I think is Rosewood herringbone in the living room and lounge, between that is the tiled blue/ white dining room floor which leads to the kitchen. As part of a kitchen renovation I want to replace the kitchen/ dining room tiles as I think the white is too stark and jarring against the wood. What colour/ type of tile would blend in better with the Rosewood, or any other flooring suggestions instead of tile?