1)
What is "Kishor"?
1.
Rashi: It is a weaver's beam [to hold the warp thread]. It enables the spindle to spin thread.
2.
Rashi (31, according to the Mashal): It is Kisharon of deeds (they are proper).
3.
Malbim (Derech ha'Muskal): It is thick wood used to incarcerate prisoners - "Motzi Asirim b'Kosharos" (Tehilim 68:7). It represents thick physicality, which ties and weighs down the Nefesh.
2)
Why does it mention Yadeha and Kapeha?
3)
Why does it say "Tamchu Falech"?
1.
Rashi: It is a support, like "u'Machazik ba'Pelech" (Shmuel II, 3:29).