1)
Why does it mention their flocks?
1.
Rashi: Their flocks grazed and consumed the grain.
2)
What had no number - the Midyanim, or their camels?
1.
Malbim: Both of them had no number.
3)
Verse 4 already said that they destroyed the land. Why is this repeated?
1.
Malbim: Here it teaches that they came primarily to destroy it.