How prepared am I to start the Higdon training?

I figure I am running an 11-minute mile. So on my long runs, I'll need to slow it down to a 12 minute mile. Running with a stop-watch really satisfies the obsessive side of my personality. Yesterday I ran 3.75 miles in 40 minutes. I don't know if I could run 6 miles like the Higdon schedule wants me to do on the first week. I don't want to injure myself, and I still have time till the January marathon. It's an 18-week program, so the latest I would start is the end of August. What's nice about running the Disneworld marathon is that I'll be used to the humidity, and it's a flat course. And come on, running through Sleeping Beauty's Castle and seeing all the characters cheering you on as you run seems like it would be more of a party than a race.