i did it 3 years ago. dont go out to hard in the beginning. The climb is a monster!! try not to use your granny gear, to much torque which lifts your wheel of the ground. just get a nice rythm and stay with that until you aqre at the top
I would suggest using any carbohydrates drink, just dilute it to half the strenght. That way you will lose some weight in the long run as long rides is normally slower and not as much carbs is needed