I want to echo that - especially as we train for these long runs, our calorie and nutrition needs can change daily; your body will let you know when it needs more! I was trudging along with far too few calories for quite a while, hoping to lose 5 pounds. I wasn't losing anything and was exhausted all the time. I finally gave up and decided energy was more important to my running goal and added a few hundred more calories a day, on average... don't ya know I feel better, my performance is better - and I've lost several pounds.
I'm a big fan of Galloway's advice: don't go into your first distance race with any time goal - just aim to finish. It's easy to get caught up in the numbers and lose sight of the bigger picture... pace has as much to do with weather/health/age/previous injuries/etc. as it does with training. Get too attached to a certain number in the beginning and you could set yourself up for monumental disappointment.
I trained for most of last year's TOT with a time goal in mind. I trained harder than I should have for my age and health status and wound up injured. I went from around a 12:00-12:30mm training pace to a 16:xx average pace in the race. It was hugely disappointing; I knew that that slow pace wasn't reflective of my capability and that it had everything to do with a knee that screamed every time I took a running step... but I was so attached to that time goal, it really did a number on my psyche. I changed strategy for the 2013 PHM; by the time it came, I had only two goals: to finish and to, hopefully, finish without pain. I accomplished both and even surprised myself with negative splits through the second half of the race. My final time still wasn't fast since I was coming back from injury, but I felt so much happier and better about myself afterward.
I guess my point is this: a time or pace goal is a great motivator, but I wouldn't make it too important for your first distance race. Nowadays, I push myself in training only so far as I know I can without inducing injury and don't set race goals until a few days prior to race day - when I know what my capabilities are, what the weather will be like, how I'm feeling, etc. I find it makes for a much happier, less stressful race experience.