From a total PBP virgin whose approach to this year's ride is not to enter at all, I just wanted to second the idea of making sure the geometry is as you expect. I shipped my bike abroad, put it in the basement, and didn't ride it for three weeks. When I rode it, after 20 miles I was sore.
It was a nothing more than me being a bonehead. When I got it out of the box I just put the seatpost in to about the right height, then stored it and forgot I'd never properly set it up. It turned out the saddle was about an inch too high. With that fixed, on my next ride I was getting sore after barely 5 miles - sliding the saddle forward half an inch fixed that.
I shudder to think what state I'd have been in if I attempted to ride 1200km.