1)
Who are "Sarei ha'Chayalim"?
1.
Radak: They are soldiers who fled from the Bavliyim. They appointed officers over themselves to conduct according to them.
2)
Why does it say "Asher ba'Sadeh"?
1.
Radak: They were in the villages.
3)
What is the significance that he appointed men, women and children with Gedalyah?
1.
Malbim: This shows that he does not want to exile more people, rather, that the land be settled. Therefore, they gathered to him.