1)
Why does it say "Ki Tov Hashem"?
1.
Radak: It is proper to praise Him because He is good and does good.
2.
Malbim: This refers to one kind of praise - due to Himself, for He is good. Also refer to 135:3:2:2.
2)
What is "Na'im"?
1.
Radak: His name - and He is His name. The verse repeats the matter in different words.
2.
Malbim (3-4): This refers to a second kind of praise - due to His creation and conduct. "Shmo" is how we know Him via His creations. Pleasantness is based on the level, order and relation between one who understands and what he understands. I.e. the fixed, ordered conduct, i.e. His name, is pleasant. It agrees with the order of Hashgachah.
