Well, for a start, it looks beautiful already - I'm a sucker for a hand-drawn map. First suggestion is to take a look around at some of the finished maps to see if anyone's already done what you're looking for...and then copy that style. Next, give us more information: do you want a painted look? Textured? Clean and bright or grungy and dark?
Have some rep for posting a map right away (and such a good one at that!)