Such major purchases are needed in order to get out front of development. The Land Bank would be a public body with the powers of condemnation. The advantages are several. Tax-exempt status for the bonds allows a lower interest rate. Zero-coupon bonds are bought at a discount from their face value and there is no interest paid until redemption.
Interest accrues over the life of the bond and is paid only at maturity.
Revenue bonds are bonds which can only be repaid out of revenues from a specific project. For example, revenue bonds used to finance a public facility such as a Tennis Center can only be repaid out of the monies generated by the Tennis Center. In the case of a Land Bank, the bonds holders could only claim for repayment would be from revenues generated by the specific land or pool of sites. Over the life of the program, the Land Bank would sell land. And it would, presumably, sell it at a substantial profit.