Hi, Tiles, paint, glass splashback or using the same worktop effect as a splashback all depends on personal choice as this is the space you will be using and seeing daily especially if you are a real foodie. If it is tiles you are wanting, I wouldnt tile to the top, I think it may be too much Especially with metro tiles; rather I'd prefer to line the tiles with the window bars and see if the extractor can be lowered by a notch to ensure there is continuing straight line through out. Alternatively, I'd consider a neutral coloured glass splashback behind the counter space which would co-ordinate with your walls and work surface.... Good Luck

I wonder whether a darker wood effect tile would work on the floor? Darker wood seems to create a more classy feel whereas the pale wood tiles (which are nice) seem more beachy.

Walls and Floors have these https://www.wallsandfloors.co.uk/white-tiles-white-floor-tiles-15072 https://www.wallsandfloors.co.uk/matt-black-white-floor-tiles-black-floor-tiles-15071

Maybe some kind of tile trim? Most of them fit half under the tiles to secure them. Or plastic strips like window fitters use to tidy up gaps. Something like this but tile shops will have a selection.