What exactly were the "Keruvim"?
Rashi (from Sukah, 5b): They had the face of a child. 1
Rashbam: A large species of bird, as in Yechezkel, 28:14.
R. Bachye: They are angels. 2 We are commanded to believe that angels exist, for they bestow Chachmah and prophecy through Hashem's command.
As a matter of fact, the word "Keruvim" really reads 'ke'Ravya', like children (Ramban). The Ramban, who hints according to Kabalah why the Keruvim faced each other and why they were 'beaten'.
Why does the Torah write "Shenayim" and not "Sh'nei"?
R. Bachye: Whenever the Torah writes "Sh'nei" it means that they are exactly similar, 1 which is the case here in most regards. Only they differed inasmuch as one had the face of a male, the other, of a female. 2 And it is to indicate that they were to be formed as a couple (and not as two individuals) that the Torah writes "Shenayim".
What is the definition of "Mikshah"?
Rashi and Rashbam: It means that the Keruvim were beaten (with a hammer [Rashbam]) out of the same lump of gold as the Kapores, 1 and not manufactured independently and soldered to it later.
As the Torah explains later (in Pasuk 19 [Rashi there]).
Rashi writes that the Keruvim had the face of a child. What is the reason?
Vilna Gaon (Chidushei Agados Bava Kama Perek 8, Michtav me'Eliyahu 5, p. 460, citing a Midrash): A young chick, its mother puts food in its mouth; when it is older, it can feed itself. A child totally depends on Hashem 1 , and there is awesome Hashgachah. When he grows, he trusts in himself, and the Hashgachah decreases. Also Bnei Yisrael feared Mitzrayim and trusted in Hashem before Keri'as Yam Suf. Afterwards, their trust and Hashgachah decreased.
Mishnas R. Aharon 4 p.70: A baby who relies on his mother and on no one else, this arouses love from his mother. Likewise, total reliance on Hashem arouses His desire to fulfill all one's requests.
Rashi (20:20) writes that one may not make four Keruvim, instead of two. Shlomo made another two (Melachim 1:6:23)!
Malbim (20:20:3): A Navi authorized Shlomo to make them.
Why can't we similarly say, the Isur is "Elohei Kesef vEi'lohei Zahav"? Shlomo's Keruvim were primarily of wood, just they were covered with gold! Rabanan permit a wooden Menorah of seven branches (Avodah Zarah 43a)! Perhaps since it looks like solid gold, it is forbidden. (PF)
How did they rest on the Aron? The Kapores covers the Aron! We must say that it rested on the gold outer covering of the Aron. Sukah 4b says that the outer covering extended above the wooden Aron, opposite the Kapores. How could a a gold wall Mashehu thick support the weight of Keruvim? Refer to 25:11:152:1*.