Medical issue should be considered and only you and your doctor can decide if there may be medical reasons to be cautious.

But I think worrying about being able to finish can create an imagined fatigue also. Develop a good base. Then find your own comfort level.

For our upcoming WI trip I'm doing just 30mi every other day with emphasis on hills, and we will average 75 - 100 mi a day. That is a low base for our mileage but is all the time I have.

In previous years there have been days where I dropped off the back of an aggressive group because I was worried I could not finish the day at their pace. Once I relaxed it became easy to maintain a comfortable pace that was almost the same as the aggressive pace.