1)
From when is the year counted?
1.
Radak: It is from when this Nevu'ah was said.
2)
What is "ki'Shnei Sachir"?
1.
Rashi: I will make the time [of their demise] exact, just like a hired worker is exact about (not to work more than) the years he was hired for (Radak - "v'Eved Yish'af Tzel uch'Sachir Yekaveh Fa'alo" (Iyov 7:2).
3)
What was the honor of Kedar?
1.
Malbim: Its great camp.