What did Moshe mean when he said "Panai Yeilechu"?
Rashi #1 (citing Targum Onkelos), Ramban and Rashbam: It means that Hashem will not send a Mal'ach, but will go with them personally. 1
Rashi #2 (citing Megilah, 24b), Hadar Zekenim #1 and Targum Yonasan: It means 'Wait until My anger dissipates'. 2
Ramban (in Pasuk 12, according to Kabalah): It means that He would lead Yisrael, via the Mal'ach ha'B'ris (Matatron) whose Gematriyah is the equivalent of Shakay. 3
Seforno: It means that Hashem will lead them to Eretz Yisrael, but will not travel in their midst.
Hadar Zekenim #2: Refer tto 33:14:2:1.
What are the connotations of "va'Hanichosi Lach"?
Ramban #1 (citing the Ibn Ezra) and Hadar Zekenim #1 (citing R. Yosef): It means that Hashem will go with with Moshe alone.
Ramban #2 (in Pasuk 12, according to Kabalah): It means that Hashem will make it lighter 1 by switching from Midas ha'Din to one that combined with Rachamim.
Rashbam and Seforno: It means that Hashem will go with them to conquer the land and give them respite from all their enemies from roundabout.
Targum Onkelos and Targum Yonasan: It means that Hashem will give them respite.
Hadar Zekenim #2 (in Pasuk 14) and Da'as Zekenim (in Pasuk 15): It means that Hashem will settle Moshe's doubt (as to whether it is good for Hashem to go with them or not).
See Devarim 25:19 (Ramban).
Why did Hashem ask Moshe to wait until His anger had departed?
B'rachos, 7a: To teach us that one should not try to appease someone in his time of anger (until it has abated).
Oznayim la'Torah: Because Yisrael needed to spend some time in Cherem to atone for their sin - just as Miriam had to spend seven days outsiide the camp before Hashem forgave her.