The City Manager shall be the chief administrative officer of the city government. He shall be selected by the Council on the basis of training and ability alone, without regard to his political or religious preferences and need not be a resident of the city at the time of his appointment but shall become a resident of the city within ninety (90) days after his appointment and shall so remain throughout his tenure of office. The City Manager shall, with the approval of the Council designate an appointive officer or employee of the city to serve as an acting City Manager who shall perform the duties of the City Manager during his temporary absence or incapacity. The acting City Manager shall serve in such capacity at the pleasure of the Council. The Council shall designate a qualified person to perform the duties of City Manager during a vacancy in the office.