Kamu is plural, but mi'Mekomo is singular!
Radak: Kamu refers to the individuals (each one rose), mi'Mekomo refers to the Klal (the army is singular).
Where is Ba'al Tamar?
Rashi citing Targum Yonasan: It is the plain of Yericho.
What is the meaning of "Megi'ach"?
Rashi: It was drawn, like "Yagi'ach Yarden El Pihu", "Gochi mi'Baten" (Iyov 40:23, Tehilim 22:10).
Radak: It leaves. This is Po'el Omed (the action applies to the subject himself), as opposed to "Yagi'ach Yarden El Pihu" (Iyov 40:23), which is Po'el Yotzei (Pi'el - he acts on others).
What is "mi'Ma'are Geva"?
Rashi: It is from a narrow place, the Ervah and exposed place of Giv'as Binyamin, from where it is easy to capture. This is like "Ervas ha'Aretz" (Bereishis 42:9).
Radak citing Targum Yonasan: It is the plain of Giv'ah.
Radak: It is like "Aros Al Ye'or" (Yeshayah 19:7) and "u'Mis'areh k'Ezrach Ra'anan" (Tehilim 37:35), i.e. moist 1 . It was a place of herbs.
Malbim: It is a cave [where the ambush was hiding].
Rashi there explained "Aros" and "u'Mis'areh" to mean intertwined and rooted well.
