Is a person considered an apostate (khariji), and do the descriptions of the Prophet (PBUH) apply to him as being "dogs of the people of Hellfire" and that there is a reward in killing him, if he possesses one or more of the characteristics of the Khawarij, or must all the characteristics of the Khawarij be present for him to be considered as such?

The Khawarij are defined by their rebellion against the Muslim community and its ruler, and by their declaring a perpetrator of major sins to be a disbeliever. Anyone who rebels against the rightful Imam, upon whom the community has agreed, is considered a Khariji. There are other characteristics that they share with others, such as ignorance, excessive worship, and reciting the Qur'an without comprehension. However, these alone are not sufficient to deem someone a Khariji.