Unless you are a pro I think most riders would find it difficult to get to the end of that ride and feel like you’ve underachieved and you’ve got plenty left in the tank! Start easily and enjoy the ride which should be an incredible experience.
The power you put out will be to a degree selected for you by the gearing you choose as much as your legs so give that some thought. They are all long climbs so start them steadily, know the length of each one before you start so you can judge your effort. As @Dave says use a HR monitor as well.
If it all goes really wrong and you find you’ve paced it badly and loads of energy left at the foot of the final climb just go for the Alpe D’Huez KOM to finish off the day 