1)
What is the difference between Tzinah and Magen?
1.
Malbim: Tzinah surrounds the body on three sides; Magen surrounds only one side.
2.
Malbim (Divrei ha'Yamim II, 14:7): Tzinah protects from a sword or spear; Magen protects from arrows.
2)
How much is a Maneh?
1.
Radak: It is a Litra, i.e. 100 of the coins we mentioned. Also in Divrei ha'Yamim II, 9:16 it says 300 Zahav. A Maneh is 300 [Dinarim] in Chazal's words, e.g. a Besulah's Kesuvah is 200, and a widow, Maneh 100 (Kesuvos 10b).