I shot the first stage of the Giro d'Italia 2010 with a 7D + 70-200 f/4 IS and the reach was perfect.
The position on the outside of an S curve gave me multiple framing options.
Since then I've upgraded to the f/2.8 IS II so that's what I would take next time.
I'm not sure if using flash would be a good idea (if allowed at all). If you do then remember to enable high speed sync.
And if you're new to bicycles races I suggest shooting a time trial, you will get a new shooting opportunity about every 30 seconds so you will learn fast.
About spectators: the bigger your lens, the more space you will get .
(asking politely works wonders too)