Moon is a sacred suffix (The first part of the name) in a warrior cat name. 'Moon' is the suffix of the Moonstone. A cat can be named Moonstone which is the name of a StarClan stone. That is why it is sacred.
Soul is an unrealistic suffix and prefix. Cats wouldn't call it a soul or a spirit. They'd rather call it StarClan spirit. But, since the cat isn't a spirit, I would call it unrealistic.
Kit, paw and star are reserved suffixes. This is what would happen if you have the suffix 'kit': KitKit would be your kit name. This is what happens if you have the suffix 'paw': PawPaw would be your apprentice name. This is what happens when you have the suffix 'Star': StarStar will be your name as a leader. It's just unrealistic, reserved, and awkward...
So, make sure you don't use these suffixes and prefixes when creating your amazing character! :3