Welcome! A fellow Dutch new-comer like myself, maybe we're a virus that is spreading.

Having no experience with CC at all, I can't really give advice on the practical aspect, but like Steel General has said, the terrain transitions are pretty sudden. You could use photoshop to blend it somewhat, though I don't think that's a small task, and it limits adaptability if you plan to change things around still.

The smaller fonts over the forests are a little difficult to read, and it might be cool if the origins of the rivers forks together from out the mountains. Aside from that, it's a pretty cool map!