Why would Edom be interested in the fact that Hashem listened to their cries?
Rashi: Moshe was referring to Yitzchak's B'rachah 1 "ha'Kol Kol Ya'akov", which had come true,
See Sifsei Chachamim.
Who was the Mal'ach referred to in the Pasuk?
Rashi: The Mal'ach was Moshe 1 .
Targum Yonasan: It refers to one of the Mal'achei ha'Shareis.
Rashi: A proof that the Nevi'im are called 'Mal'achim' - as we find in Divrei ha'Yamim 2, 36:16.
Where exactly was Kadeish?
Rashi (Ibid.): From which point they were about to begin their entry into Eretz Cana'an.
Why did Moshe tell Edom all this?