When was Moshe instructed to perform this task?
Rashi: Although he was issued with the instructions now, he was only to carry them out later, after the completion of the construction of the Mishkan. 1
Having stated "Aharon and his sons", why did Hashem see fit to mention them all by name?
Ramban: To teach that they all required individual anointing, and should not rely on the fact that Aharon was anointed and they were his sons. 1
Why does the Torah say "Lechahano Li"?
Da'as Zekenim: Whenever it says Li, it means forever - "Ki Li Kol Bechor", "Ki Li Bnei Yisrael", "Ki Li ha'Aretz."
Ibn Ezra: The 'Vav' in "Lechahano" is superfluous. 1