Chiming in too...
Agree with many points - mainly, trying out your lighting gear ahead of time. I did a 300K that I would only be in the dark for a few hours. Well, dark is dark, no matter how long it's gonna be. I didn't have strong enough lights to see far enough ahead on descents, and I didn't have any helmet light. When you start hearing rustling in the brush next to the road, it's nice to be able to look and see what it is. Or isn't.
And, plan out the runtime of your lights and add a few hours of cushioning - lots of things (temperatures) can effect how long battteries will run. If your controls are at stores, think about lights that use AA batteries so you can easily stock up.
And have fun!!!!!
For 3 days, I get to part of a thousand other journeys.