Throw all the advice at me, I don't know what I don't know.
I'm going to use the Hal Higdon novice plan and will start in August. I stay in half marathon shape all year round, averaging 30-35 weekly miles. My last two HMs this spring was around 1:47 and I'm really hoping I can do a sub 4 marathon in December. Am I being realistic? I know a marathon is 4x as hard as a half and the longest I've ever ran is 15 miles.