What a great idea, that's fantastic! :) Such a brave challenge to take on, really not for the faint hearted; credit to you. With all the good training you're putting in, you'll be well able for it by 2019. I haven't read it myself yet but several of my running friends recommended the book Born To Run; they said it was a great inspiration in them going on to run long distances races and gave them a new perspective on training. It may be a nice read for you before you're properly on your way with 2018's miles.