When maps, profiles, and estimates are filed, the board shall issue an order directing the issuance of bonds sufficient to pay for proposed improvements together with necessary, actual, and incidental expenses. The bonds may not be issued in an amount greater than the amount specified in the order and notice of election, and in districts operating under Article III, Section 52, of the Texas Constitution, the bonds may not be issued in an amount greater than one-fourth of the assessed valuation of the real property of the district.