This year we went to the finish in Alpe d'Huez, the start the next day in Bourg d'Oisan and to the finish in Paris and had no trouble sorting it all out ourselves. It was a fantastic family holiday, with my wife and 3 year old son coming along too. You see more on tv, but seeing Le Tour up close is unforgettable.
Somewhere like Alpe d'Huez is easy - you camp... absolutely anywhere! We stayed on a bit of grass in the town and toilets and water supplies were made available by the local council.
In Paris we had no trouble getting a hotel room only a month before the race.
If you want to book hotels in other places though it's best to be on the phone the day of the route announcement - check www.letour.com later this year - it's normally about October I think.
Good luck and enjoy yourself - I had great fun climbing some legends like Alpe d'Huez and Mont Ventoux and then retiring to a bar to watch the tour on tv for most of the time!