I agree with comegetme about getting samples together in the actual kitchen space. The reason why I prefer the lighter one is the pattern. Even though I really like the pattern in the darker one as a single tile, I think that the floor will end up with too many fairly clear lines running crisscross, or if they're laid in the same direction, the lines will never match. I think it would drive me bonkers. Whereas the marble effect tile has a softer and less linear pattern. But it might not be a problem for you :-)

I don’t feel a prospective buyer would worry about one cracked/broken tile to be honest. Nowadays people usually update a new home to their own taste. I would remove the tape unless it is a trip hazard as that will only make it look worse.

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.