Heir to Magic

I have not had a chance to work on Heir to Magic, but, I have worked on the Heir to Magic outline and my plans for the story. I want to make this a trilogy, I have always seen it as a trilogy, but I have not yet determined the exact sequence of how that will work. I have started with a notebook and am going to be working on just what I want the trilogy to cover, then I will be better equipped to know if I really am writing the first book, or if I have started at the second book in the trilogy. I know that sounds weird, but if you saw the story line I ain't sharing then you would understand better.