1)
Who says "Keli Atah v'Odeka"?
1.
Rashi (27, citing Pesachim 119a): David said this when Shmuel anointed him.
2.
Radak: Yisrael say, it is proper for me to thank Hashem more than all the nations, for You are Keli - You showed Your strength and ability via me. You took me out of Galus with Your great strength.
2)
Before, it said "Keli Atah." Why does it say now "Elokai"?
1.
Radak: You executed my judgment against the nations.
3)
What is the difference between "v'Odeka" and "Aromemeka"?
1.
Malbim: I will thank You for the good, and elevate You to tell Your general praises.