On the eating and drinking thing the one word of caution I can give is be careful not to over estimate how much you need. For my first marathon I think I was eating for a family of six, as I though that was what I needed to fuel my runs!
My own personal opinion is that if you're diet is reasonably healthy then you don't really need to adjust it. For long training runs like your 18 miles you do need to use the time between now and Paris to find out what works for you as a pre-run meal. For many that is porridge. I actually seem to run well off crunchy nut cornflakes. Ultimately it's trial and error until you find something that works for you. The same approach for race fuelling. Try a few different brands of gels, or shotbloks, or other foods you can eat on the run and see what sits well in your stomach while you run.
Another thing is don't worry about that 18 mile slog, Been there, done that. In fact just the other weekend I had one of those training runs and I could have happily quit at any mile along the way. A real slog from start to finish. It's just a thing of doing a long marathon training schedule. Sometimes no matter what you have a day where it just feels like hell from start to finish. Those runs are great for building up the mental toughness. Other times you'll get a surprise feeling good run and it'll boost your confidence.
As someone new to the distance I'd expect you're first few long runs like that 18 to be a slog. Your body isn't used to that distance yet and you'll still be working out what is best to eat pre-run and during the run.
Andy - That's still some very impressive mileage you've racked up over the last few years.
Pancake - Don't worry about some of us having more experience. We all started off somewhere and some of us with far more idiotic plans than others!
The marathon is a daunting distance, but you'll get to the finish. There are few more memorable moments than completing your first marathon and the feeling of knowing that you did something that even on the start line you doubted you could do.
It's also worth remembering that while it's good to read about other peoples training on here, just because some are doing more miles, or going faster, doesn't mean you aren't doing enough or can't talk about your training. Everyone is at different levels, different experience and many started exactly where you are now.
The thread has been great over the years at supporting people in achieving their goal, be that to finish or going for a specific time. You've picked a great race for your first marathon.
Jimbob - That Amsterdam 2010 sub-4 failure seems like a lifetime ago now. I've been sub 4 on my last five marathons, including surprisingly coming well under it at Portsmouth where I wasn't expecting to run well. First time I've ever ran a negative split at a marathon too!
Natty - Glad to hear your getting back into a regular routine. Long may it continue.
Nodster - I'm well jealous of the places you're going too. Less so on the ultra running part.
I run four times a week, occasionally five if I meet up with the massive for a park run or my football is cancelled. I play football once a week, which I don't count as training.
My typical week is: Monday - Football, Tuesday/Wednesday/Thursday - Run, Saturday - LSR. My midweek runs tend to be around the 10/9/6 miles in length. This week for instance I ran 9 miles on both Tuesday and Wednesday and 6 miles last night. I occasionally throw in a 5km run, which is an all out out make me want to die in agonising pain run.
My structure isn't what you'd find in any plan though. I do all my midweek runs hard. All of them I'm pushing as hard as I can. For my LSR I just jog around at a pace I feel comfortable at. I never look at my watch for pace or time on any training run. I just check my times pace when I finish the run.
Interestingly enough I tend to run faster on the Thursday than I do on a Tuesday, which seems wrong as I would think I should be getting fatigued! I also have run better marathon times when my LSRs have been slower. The times when I've ran fastish LSR's without trying without fail I've ran badly in the marathon. It's my midweek run pace that is the key indicator to me where my race day pace is at.