1)
Why did he make copper shields?
1.
Malbim (Divrei ha'Yamim II, 12:10): It was for Teshuvah, to always remember that due to his sins, the gold shields of his father, which were glory for him, were taken.
2)
What are "Ratzim"?
1.
Radak (Shmuel I, 22:17): They are people who run on foot in front of the king.
