Thanks, John.
The museum owns somewhere in the neighborhood of 22 miles of ROW, to the north and south -- but it is not 100% continuous. There are small sections of the ROW which are privately owned in both directions, but so far each land owner has agreed to easements for the railway. For now the plan is to build another couple of miles north, to Rt.218, and see where things stand. Crossing Rt.218 and continuing to Head Tide is one option, but the possibility also exists to build south toward Wiscasset. Going south would mean crossing "Cross Rd.," but would enable the museum to add another couple of miles and to reach Wiscasset proper, although shy of the waterfront. James P. can give a better idea of how close and what obstructions exist to the south, but from what I understand the next privately owned section of ROW is 2-3 miles south of Sheepscot station.
Happy New Year!