1)
Why did he mention Balak?
1.
Malbim: Balak was king at the time, and he was silent, and so were the kings after him, for 300 years. This is Chazakah with a claim!
2)
What is the meaning of "ha'Rov Rav"?
1.
Radak: He quarreled.
3)
What is the meaning of "Nilchom Nilcham"?
1.
Radak: The first is with a Cholem. It is Makor (not a conjugation, rather, like an infinitive, to fight), like "Nish'ol Nish'al" (Shmuel 1:20:6), and the latter is Nif'al (passive), in past tense.