This act shall be construed as cumulative authority for the exercise of the powers granted under this act. The purpose of this act is to create full and complete additional and alternate methods for the exercise of these powers, and the powers conferred by this act shall not be affected or limited by any other statute or by any charter or incorporating document, except as otherwise provided in this act. However, this act does not authorize the governing body of any governmental unit to levy taxes in excess of constitutional, statutory, or charter limitations without the approval of its electors, as provided by law.