The Gatorade is OK, I wouldn't worry about it too much, it's not that much different to the stuff you can buy in the shops...... depends who's mixing it. I will probably stick to gels and water though.
As for the Haloween parade,,,, American's think that fancy dress is wearing a bow tie and cumberbund.... They call a fancy dress party a costume party!! Typical of the Yanks to screw with the English language
I did Luton once!! Only one loop though as I was part of a relay team. If I recall, it wasn't that bad Anyway, you will see plenty of concrete in November!!
I don't like hills either, but I'm use to the ones in NYC. The worse bit on the marathon is probably the 59th Street bridge as it just goes on and on at a gradient which will raise your heart rate just enough to hurt. Still, at least you get to run downhill and look good for the crowds when you enter Manhattan.
Rob - Welcome!! I would say that you would be better off running six miles before the race, then doing the 16 miles at your long run pace and not racing it. It is more beneficial to get that last very long run in than doing a race..... It's all about time on your feet.
Also remember it takes approximately 1day per mile raced to recover so if you race the 16 miles, it will take 16 days to fully recover - this will bring you close to the marathon date and could upset your ability to get the final few long runs in prior to New York.