did 2013, a cheerful and strong riding/training partner was a big help and support, we did an SR with a few extra rides thrown in plus commuting. We tried overnight riding on a diy 600km and decided we did not like it. So we used an excellent spreadsheet someone supplied on here to plan our days. In short had to be up at 3am to ride at 3:30 odd until about 10pm. The controls were almost all godsends bar the odd bad one, and we scoffed hot food in every one. As someone said then, 'only 4 300ks with a 250 to finish'.
Physically we were fine barring sore knees by the end but mental fatigue did start to get dodgy on the last day, hallucinations etc. This was not helped by some farily crappy weather on the last 24 hours, rain and a shocking hot day with a stern headwind.
As for navigation, we had the routesheets and a gps but there were so many other rider you almost always had a clear sense of the route.
If you're thinking of having a go, do it. any issues with fitness and bike setup will get sorted in the training, not sure I'd have made it solo and saw a few other fellas I knew that were doing it solo looking sorry for themseles on days 3 and 4.