Advice given to me when I first made the jump to 400's, and has served me well in further jumps since.
1, Don't over analyse it. Turn up, ride bike, sleep when needed, eat when needed. Repeat until end
2, Don't think about the total distance, only the distance to your nest stopping point. Thinking about the distance to the end play on your mind too much. Split it into smaller chunks.
3, Probably the most important, make sure you never put in maximum effort. Even on the hills, always ensure you leave something in reserve.
Keep that in mind, and I'm sure you'll be fine.