When the governing body of a municipality adopts a resolution as provided in this chapter, it shall promptly notify the mayor of such adoption. If the resolution adopted is one approving the exercise of powers hereunder by a slum clearance and redevelopment authority, the mayor, by and with the advice and consent of the governing body, shall appoint a board of commissioners of the authority created for such municipality which shall consist of 5 commissioners, and when the governing body of a county adopts such a resolution, the body shall appoint a board of commissioners of the authority created for such county which shall consist of 5 commissioners. The commissioners who are first appointed pursuant to this chapter shall be designated to serve for terms of 1, 2, 3, 4 and 5 years, respectively, from the date of their appointment, but thereafter commissioners shall be appointed as aforesaid for a term of office of 5 years, except that all vacancies shall be filled for the unexpired term.