Why does it say "u'Min ha'Ir..."?
Radak: Everything mentioned above, he took it from the Beis ha'Mikdash.
What is the meaning of "Seris"?
Refer to 8:6:2:1.
Here it says "five from those who see the king." In Yirmeyah (52:25), it says seven!
Radak: Two of them were not as great as the five, therefore they are not counted here.
Radak citing Yerushalmi Sanhedrin 1:2: In Yirmeyah it includes two scribes of the judges.
Malbim: First, he found five. Later he found another two, and there were seven.
What is "ha'Sofer Sar ha'Tzava"?
Rashi: He knows for each city the number of men it brings to the army.
What is the meaning of "ha'Matzbi Es Am ha'Aretz"?
Radak: People go out to the army according to his command.