Why does it say "Hashem Elokei Tzevakos"?
Radak: He is the G-d of legions of Shamayim, and rules over them.
Malbim: "Elokei Tzevakos" is the natural conduct via the Ma'arachah and legions of Shamayim.
Why does it say "Mi Chamocha"?
Radak: Among the upper beings that exist forever, who is like You?! They testify about themselves, that their entire existence is from You, who exist forever!
What is "Chasin Kah"?
Radak: Chasin is strong, like "v'Chason Hu ka'Alonim" (Amos 2:9). It is not Samuch [to Kah]; its grammatical form is like Gevir. Kah hints that Hashem brought the world into existence; it is from Him. He perpetuates the world after He made it; He is called Chei ha'Olam.
Malbim: This refers to strong, fixed conduct.
Why does it say "ve'Emunasecha Sevivosecha"?
Radak: This is like it says "Emunasecha bi'Kahal Kedoshim" (verse 6). The Kadosh angels are around Him, and they testify to His Emunah, i.e. His existence.
Malbim: Also natural conduct, which is based on Emunah, is around You; You dwell among the legions of Shamayim, and act on them.