(1) The board of county commissioners shall use the proceeds of such sale in making payment for the cost of the improvements. Payments to contractors may be made either from time to time, on estimates made by the engineer in charge of such improvements for the county, or upon the entire completion of the improvements and the acceptance thereof by the board.
(2) All interest earned on the investment of bond or warrant proceeds during the construction of improvements must be credited to the construction account of the improvement district fund from which the proceeds were withdrawn.
(3) Any proceeds of the bonds or warrants, including investment income thereon, remaining after payment of all costs of the improvements must be transferred to the sinking fund in the improvement district fund and applied, to the extent possible, to the prepayment and redemption of bonds or warrants on the next succeeding redemption date for which notice of redemption may properly be given.