> Q: How long is "too long"? If you're English and the Pope calls for a crusade against Egypt, can you walk all the way through France, Germany, Turkey?

Keep it moving, staying in the same place for more than 2 turns is a bad idea.

Q: If the Pope calls for a crusade, what are the ramifications of obeying or ignoring him?

Pope's crusade are free, the pope will like you more. Feel free to ignore him.