No advice, but I'm right there with you with the first marathon thing. My first is in a couple of weeks (June 10th)! Already got in the 20-miler, etc., and am now tapering...kind of...going backpacking this weekend and considering that the last of my major "running" until the race.
Best of luck to you, and I can't wait to hear about it! There's a little used tag, #racereport where you can read up on what some of us such as WanderingEng and Creativity have been up to. But probably the most intriguing are the various endeavors of wasoxygen.