1. Reign of Terror or Terror would be much more appropriate. Although the Great Terror is not wrong, it also refers to the Great Purge by Stalin and a book that deals with Stalin.
2a. Marie Antoinette surely said many things but "let them eat cake". Maybe adding the word "allegedly" or "was attributed to" would be more appropriate for historical convenience.
2b. It's brioche, not cake.
3a. Jean-Baptiste de Villèle is more offen referred to as Joseph de Villèle.
3b. Please mind the direction of the accent in "Villèle".
The "alleged" word in english is cake. it's a common phrasing as well as famous expression. Don't forget, like you said, it is a myth and this is the english version of eat.
2a. Marie Antoinette surely said many things but "let them eat cake". Maybe adding the word "allegedly" or "was attributed to" would be more appropriate for historical convenience.
2b. It's brioche, not cake.
3a. Jean-Baptiste de Villèle is more offen referred to as Joseph de Villèle.
3b. Please mind the direction of the accent in "Villèle".
4. Duc de Berry, not Berri.