If there was only one piece of advice you could give what would it be and why? I ask this because I know from past marathons that when you're really tired your brain goes to mush and it's really difficult to think straight.
Just seen this. Do you belong to a running club? If not I can recommend Northampton Road Runners, I've been a member since 2004. It's the most friendly running club in Northamptonshire where you'll get lots of good advice and help to plan your marathon training. Why not have a look on the website (google Northampton Road Runners) and come along, you'd be made very welcome.
Look at the Runners World ultimate schedules, they're much better and they give really good extra info - just pick one close to the time you hope to finish in. Looking at your half time I would go for sub 4.30 plan and adjust the paces to suit. Also remember that's its only a guide - they can be adapted. That's what I do and it does work so all the best.