(2) The department may determine the housing authorities participating in the program; provided, however, that the total number of authorities shall not exceed 4. To be eligible to participate in the program, a housing authority shall be a regional housing authority under section 3A. Not more than 3 of the participating housing authorities shall have not fewer than 7 participating communities and portfolios of not fewer than 750 state-aided public housing units. Not less than 1 of the 4 authorities shall have a portfolio of between 250 and 700 state-aided public housing units and not fewer than 10 participating communities. In selecting participating authorities, the department shall establish criteria that provides for representation of housing authorities having various characteristics, including housing authorities serving urban, suburban and rural areas and housing authorities in various geographical regions throughout the commonwealth. The department shall create a position within the department to provide assistance to housing authorities during the process of becoming a regional housing authority under section 3A. Nothing in this section shall prohibit participation by an otherwise eligible housing authority on Nantucket Island or Martha's Vineyard.