Hey Matt,
Just noticed this post. I don't yet have the technical skills to improve your map much. But I am curious: What is the intended use of the map? Just as the setting of a campaign with your friends, or something more? I usually use the galleries here to give me ideas or use as the basis of a D&D campaign with my own group of friend. If it is just for personal use, it does strike me that as I was searching the galleries this morning that their are dozens of island maps. You might want to find one that is similar to what you want and asks the artists permission to use it. If you upload their map into photoshop, your could pretty easy change the names of the cities and slightly modify your story. I'm sure many of the artists wouldn't mind you using their map as long as you credit them and it is for personal and non-commerical use. But make sure you get their permission before you make any changes to their work and of course don't try to pass it off as your own.