I'm working from an Excel sheet here, that has precise number of hexes for the provinces (red borders) and terrain type within each province.

I started by creating an appropriately sized hex grid and filling it with the right amount of land hexes. Those I divided into the provinces (I had a rough outline for their position from my customer). This is the result:



I then drew the region borders and put in hex symbols for the different terrain types according to the excel sheet. The trick here is to build clusters of terrain that you can turn into 'organic' landforms later, e.g. build the mountain and hill hexes in such a way that they give a realistic-looking mountain range.



I then used this map as a reference for drawing the actual map. I created a custom style and all the landforms as drawing tools, which made the work a lot quicker and easier. I just LOVE the new forest drawing tools in CC3.