I did the Full Moon a few months after being diagnosed with type 1. The atmosphere was great and I thoroughly enjoyed the event.
As I have type 1, I cannot advise on nutrition for you. However, I would recommend practice of a similar distance and trial what you choose to eat, carry and wear. I remember lots of drink stations along the way with some food although I took my own. There were toilets ever 2 miles but the queues were long until the 14 mile mark (when the Half Mooners had left and their were less walkers)
The hardest thing for me was lack of sleep fo 36 hours. Depending where you live you may get some after your Half Moon but I did not get home until Sunday lunchtime
Have fun and raise lots of money for a very worthy cause.