In my experience, half of the purpose of building up your long runs is fitness and the other half is just learning how your body reacts to the new stress, and you are way over thinking things. This sounds like your first marathon, correct? You are taking a shit ton of electrolytes for one, stop that. If it was raining the whole time you're not going to be sweating nearly enough to plow through 16 salt pills. Don't worry about how many calories you're going through either, your body can store more than enough fuel to get you through a marathon without needing replenishment. Basically eating while you run a race of this distance is just to keep you from bonking after 2.5-3 hours or exertion (insert something here about glycogen storage or whatever...) not to fuel the entire run while you're doing it. The important thing now is to see what works for you personally as far as what works best for your nutrition and also try to get in higher weekly miles for the next two weeks if you can before tapering. 40-45 is a bit low.