1)
Why does it say "k'Yad Elokeinu"?
1.
Rashi: When Hashem's success was on us.
2)
What is "Ish Sechel"?
1.
Rashi: A Chacham. Ibn Ezra, Malbim - the verse does not name him. Perhaps it is Shereveyah,
3)
Who were Shereveyah, Chashavyah and Yeshayah (verse 19)?
1.
Rashi: Also they were Leviyim.
2.
Ibn Ezra: Shereveyah is the Chacham. The prefix Vov is extra, like "v'Ayah v'Anah." It is better to say that the Vov adds a matter. It means, Ish Sechel Shereveyah; and Shereveyah, his sons and brothers were 18.
