1)
Why did he say "Rivah Rivi"?
1.
Malbim: Regarding evil via people, wage my battle and redeem me from their desire to kill me.
2)
What is the meaning of "l'Imrasecha"?
1.
Radak: This is like Ba'avur (for the sake of) Imrasecha. I.e. I request life in order to guard Imrasecha, and not for worldly pleasure.
2.
Malbim: Redeem me due to Your words - You promised me via a Navi that I will reign.
