Subject to the limitations of the petition for its creation and all amendments thereto, an agency may own, construct, reconstruct, purchase, lease, or otherwise acquire, improve, extend, manage, use, or operate any electric light and power plants, lines, and systems, either within or beyond, or partly within and partly beyond, the boundaries of the participating municipalities, and may engage in, transact business, or enter into any kind of contract or arrangement with any person, firm, corporation, state, county, city, village, governmental subdivision or agency, the United States, or any officer, department, bureau, or agency thereof, any corporation organized by federal law, or any body politic or corporate, for any of the purposes enumerated in this section, or for or incident to the exercise of any one or more of the powers enumerated in this section, or for the generation, distribution, transmission, sale, or purchase of electrical energy for lighting, power, heating, and any and every other useful purpose whatsoever, and for any and every service involving, employing, or in any manner pertaining to the use of, electrical energy, by whatever means generated or distributed, or for the financing or payment of the cost and expense incident to the acquisition or operation of any such power plant or system, or incident to any obligation or indebtedness entered into or incurred by the agency. In the case of the acquisition, by purchase, lease, or any other contractual obligation, of an existing electric light and power plant, lines, or system, from any person, firm, association, or private corporation by any such agency, a copy of the proposed contract shall be filed with the Nebraska Power Review Board and open to public inspection and examination for a period of thirty days before such proposed contract may be signed, executed, or delivered, and such proposed contract shall not be valid for any purpose and no rights may arise thereunder until after such period of thirty days has expired.