Great map SK. One minor point ( that you were probably already planning on fixing ) is that the rivers all dead end before reaching the ocean.

As one of the mappers whose maps use a lot of objects and textures from other sources, my point of view is that the only thing that matters is the final product. Your artistic contribution is choosing the right components and how well you put it together. That is far more important than where the pieces come from. A map made entirely from scratch is no better or worse than one made from outside sources. The end result is all that matters.
Look at it from this viewpoint: Ferrari makes some great cars, automotive works of art, but they do not make all the parts, they get them from many other companies. The only thing anyone cares about is that it is a Ferrari.