Such refunding bonds shall bear such rate or rates of interest as may be determined by the governing body, not exceeding, however, six percent (6%) per annum payable semi-annually; shall be in such denomination or denominations and form as may be determined by resolution or order of the governing authority; and shall be executed in behalf of the subdivision by such officer or officers thereof as may be determined in such resolution or order. The interest to accrue on such refunding bonds shall be represented by coupons to be attached thereto, which may be executed by the facsimile signature of such officer or officers. All such bonds shall be made to mature serially, beginning not more than five (5) years and running not longer than thirty (30) years after their date, with not less than one percent (1%) of the total issue to mature each year during the first six (6) years, beginning in the fifth year, after the date of such bonds; not less than three percent (3%) of the said total issue to mature annually during the next succeeding ten-year (10-year) period of the life of such bonds; and not less than five percent (5%) of said total issue to mature annually during the next succeeding ten-year (10-year) period of the life of the bonds.