1)
Why does it say "ha'Am ha'Milchamah"?
1.
Radak: It is as if it said ha'Am Am ha'Milchamah. We find like this elsewhere
2)
What is "Neged ha'Ir"?
1.
Malbim: It is to the north, for the gate of the city was in the north.
3)
What and where was the Gai?
1.
Malbim: It was a valley between Yisrael and the city.