Looks fascinating! Btw, are you only working on this map or are you working on multiple maps at once?
I think I have some 5 maps or so that I am working on to a serious degree and many more that are in a basic stage with just 1 texture and an imported load.ini and actors. These are however flyable. I can make one of the basic maps from a DEM in around 30-45 mins. But 1 texture only to see how the terrain looks. Flat terrain is mostly out because it requires textures that don't tile into patterns. Mountains are better looking and texture more esthetically with less tiling apparent.
I've 2 more maps that are for all purposes finished right now, but which need a few small touches that can only be found by repeatedly flying around in them. I'll get these 2 out in a short while. One is of the South China Sea off the coast of Vietnam and another is in a fictional land with a predominantly green and forested and farming look.
And then it all depends on how the texturing goes on the others. Sometimes it goes so smoothly like with the recent far North map and other times I go through 10-12 or more sets of textures before it meshes together on a map. And I try to make each map with mostly a different set of textures if possible, this to give some variety to the landscapes.