I think the longest that's ever been recorded on my computer during a 24hr race was just over 22hrs. Obviously the more the better!
I've always tried (and often failed, but that's a wholly different story) to not "stop" properly - if you sit/lie around for long you'll start to seize up and it'll be twice as hard to get going again.
Your body will probably try to shut down in the wee small hours - eating will be difficult, concentrating will be hard and you'll probably have some shocking laps with awful riding. It's OK, it's part of the challenge - during the part you have to start really telling yourself to MTFU 
Remember: you *can* keep going, even though your body has convinced you that you can't...it IS meant to be that unpleasant 
If you can find someone to help out it can be a great help but, when it comes down to it, it's you that has to be hard. I'm sure you'll have no serious problems. I also reckon there'll be a great atmosphere in the pits with everyone being in the same situation.
Tow bike would be good, not essential unless you're really in it to win it during a muddy race, but helpful. If you can keep as many of the parts interchangeable, but it's no biggie.
Eat anything you can, anything is better than nothing and don't force down gels and sickly bars making yourself feel ill. Come those early morning laps when your body is revolting against still being up and riding the energy in a babybel you managed to eat will be better than the mega-nutrients in a powerbar that still in your jersey pocket
