If you're doing the Tour de Cure, no need to worry about what bike you ride as long as it is comfortable, reliable, and suitable for the terrain. Your FX will be just fine and will fit in with many of the other bikes there. TdC isn't a race and they allow plenty of time and have great support. At the starting line, you will notice that there will be a number of roadies with kit and carbon fiber who take off like a shot and you won't see them until the after party. There will be a much larger pack of recreational cyclists who are there for the fun. In this group you will see a diversity of bikes, including road, touring, fitness, commuter, CX, and slick tired MTBs. I ride an old steel flatbar touring bike for charity centuries and have a great time and don't feel the least bit out of place.

The TdC training information is a good general program that will prepare you well. If you are new to this, remember that your improvement comes not during the riding, but during the rest periods inbetween. If you notice your progress stalling take a day off once in a while and be sure to included some relaxed "recovery" rides.