Why did Hashem now speak to Aharon as well?
Rashi and Ramban: Because, following Moshe's complaint regarding his speech defect, Hashem sent Aharon together with him to act as his spokesman. 1
What does the Torah mean when it writes that He commanded them regarding the B'nei Yisrael and regarding Pharaoh ... ?
Rashi #1: He commanded them to lead Yisrael with gentleness 1 and Pharaoh with respect.
Rashi #2 and Ramban #1 (citing the Ibn Ezra): He commanded them with regard to the matters concerning Yisrael and his Shelichus to Pharaoh, which the Torah will detail later (from Pasuk 29 and onwards).
Ramban #2 (on Pasuk 12): The Pasuk means that Moshe and Aharon should speak to Yisrael and tell them whatever Hashem would command them; and Pharaoh to send Yisrael out of his land.
Seforno: Hashem appointed Moshe and Aharon princes 2 over Yisrael and over Pharaoh - creating an aura of Divine authority that forced Yisrael and Pharaoh would obey their every command concerning the redemption.
Moshav Zekenim (verse 12): He commanded Bnei Yisrael to leave Egypt, and Pharaoh to expel them, even if they do not want to go.
Hadar Zekenim: He commanded them for the sake of Bnei Yisrael, that they go to Pharaoh and tell him to expel Bnei Yisrael.
What are the implications of the word "Tamid"?
Rashi: The Kohen Gadol is obligated to bring this Korban every day.
Why do we find "va'Ydaber Moshe" to Hashem only here, and in Bamidbar (27:15)?
Hadar Zekenim: Here, Moshe asked whether or not Hashem will redeem [Yisrael]. There, he asked whether or not He will appoint a leader over Yisrael [for after Moshe dies].