1)
Here it says "ha'Chag? Shiv'as Yamim." In Melachim I, 8:65 it says "Shiv'as Yamim v'Shiv'as Yamim"!
1.
Malbim: Perhaps Ezra revealed here that the seven days before Sukos were not called Chag, and Melachah was permitted. If so, we can say that they fasted on Yom Kipur; Chazal (Mo'ed Katan 9a) expounded unlike this.
2.
According to those who say that also the days of inauguration were called Chag, the Navi teaches only this, for it is a Chidush. It is no Chidush that Sukos is called Chag! (PF)
2)
Why does it say "mi'Levo Chamas Ad Nachal Mitzrayim"?
1.
'Rashi', Rashi on Melachim I, 8:65: Levo Chamas is in the north of Eretz Yisrael. Nachal Mitzrayim is opposite it, in the south (Bamidbar 33:5-8).
