The county planning board may employ experts and pay for their and such other expenses as may be deemed necessary for the making of the master plan and for the carrying out of such other duties as are herein prescribed, except that such board may expend only such sums as may be appropriated by the board of chosen freeholders or be placed at its disposal through gift. The making of the master plan shall be regarded as essential preliminary studies incidental to the later carrying out of capital improvement projects over an indefinite period of years and may be funded by serial notes or bonds to be issued by the county, the terms of which shall not exceed five years.