What is the significance of 'meat at nighttime'?
Rashi: Refer to 16:6:1:1.
Yoma, 75b: To teach us Derech Eretz
See Torah Temimah, who gives a reason for this/
Why did Moshe say "Lechem Lisbo'a", but "Basar Le'echol"?
Rashi and Seforno: The Torah is teaching us Derech Eretz - that it is in order to eat one's bread (which constitutes one's staple diet) to satisfaction, but not one's meat, which is a luxury. 1
To break with the way of the Egyptians, who cared only about self-indulgence (Seforno).
Why did Moshe add "bi'Shemo'a Hashem es Telunoseichem", which is obvious?
Seforno: Moshe explained that part of his Tefilah was that Hashem should send food in such a way that Yisrael should realize that their complaints were against Him (and not against Moshe and Aharon), and that He had now answered them.
Why did Moshe need to say "Lo Aleinu Telunoseichem ki Al Hashem"?
Rosh (Bamidbar 16:25): This teaches that anyone who argues with his Rebbi, it is as if he argues with the Shechinah.