All moneys received from the issuance of any bonds herein authorized shall be used solely for the purpose (or purposes) for which issued, including without limiting the generality of the foregoing, the payment of preliminary expenses; provided, however, that any unexpended balance of such bond proceeds remaining after the completion of the acquisition of [or] improvement of the project or part thereof for which such bonds were issued shall be paid immediately into the fund created for the payment of the principal of said bonds and shall be used therefor. The validity of said bonds shall not be dependent on or affected by the validity or regularity of any proceedings relating to the acquisition or improvement of the project for which the bonds are issued; and the purchaser or purchasers of the bonds shall in no manner be responsible for the application of the proceeds of the bonds by the municipality or any of its officers, agents and employees.