Why did Hashem insert the word "mi'Zeh"?
Targum Yonasan: He was ordering Moshe to take the people away from the location of the sin, before He destroys them in His anger, 1
Why did Hashem instruct Moshe to "go up to the land"?
Rashi: Because Eretz Yisrael is higher than all other lands.
Rashi #2: Seeing as, when He was angry with Yisrael He ordered him to go down, 1 now that He had 'forgiven' them, He ordered him to go (back) up.
Why did Hashem refer to the people as "ha'Am" and not 'Amcha', like He did above (in 32:7)?
Because there He was referring specifically to the Eirev Rav, 1 whom Moshe had personally taken out of Egypt, whereas here He was referring to Yisrael as a whole, whom Moshe had taken out of Egypt in his capacity as Hashem's Shali'ach.
Why did Hashem mention the Shevu'ah to the Avos?
Moshav Zekenim: The plague helped atone for their sin, so now He mentions Zechus Avos, and He will fulfill the Shevu'ah