Quick snapshot (apologies for the rather odd lighting) of progress to date.
I've put a couple of layers of plaster cloth and a skim coat of plaster over the open areas that will eventually be farm and pastureland with a few scattered trees. The background hills are the green florist foam. The tan splotches are Sculptamold patches and fills - this hasn't worked as well as I wanted, so I'm going to use a Sculptamold/Celluclay mixture to try and fill some of the unnatural low spots in the plaster subsurface. Then everything will get a coat of flat latex paint.