The agreement shall specify the composition of the governing body of the joint agency or authority created under § 5.1-2.18; provided, however, that the membership thereof from this Commonwealth shall be the same as the membership of the Board created by § 5.1-2.1. Each joint authority shall select officers for such terms as are fixed by the agreement and shall have the power to employ such agents and employees as it may require and as are reasonably necessary in carrying out the purposes of this chapter. Subject to the limitations and restrictions hereinafter set forth, such joint authority shall have the powers set forth in § 5.1-2.2:1.