What is the meaning of "Velakchu min ha'Dam"?
Rashi: They performed Kabalas ha'Dam (not by hand, but) into a bowl (See Pasuk 22).
Where exactly did they place it?
Targum Yonasan: They placed it on the outside both of the houses where they ate and of the rooms where they slept. 3
Seeing as "Mezuzos" is plural and 'the minimum of plural is two', why does the Torah add the word "Sh'tei"?
Menachos, 34a: To teach us that whenever the word "Mezuzos" appears (minus the second 'Vav') it means 'one'. Consequently, one is obligated to fix a Mezuzah even if there is only door-post. 1
See Torah Temimah, note 54
What is the "Mashkof"? Why is it called by that name?
Rashi: Mashkof is the lintel, so-called because (Shakof means to bang and) the door bangs against it. 1
Why does the Torah write "al ha'Batim" in the plural?
Pesachim, 86: To permit the owners of a Korban Pesach to divide into two groups and to eat it in two locations. 1
See Torah Temimah, note 57.
Hashem told Moshe "Al ha'Mezuzos v'Al ha'Mashkof." When Moshe told Yisrael (verse 22), why did he say "Al ha'Mashkof v'Al Shtei ha'Mezuzos"?
Riva citing R. Yosef of Paris: Moshe deviated, lest people say that both are required only when one puts on the Mezuzos first, but if puts on the Mashkof first, this is enough, for in any case blood will spill onto the Mezuzos!
Moshav Zekenim (22) #1: The blood on each Mezuzah is like the letter Yud, and on the Mashkof is like Vov. In all, their Gematriya is 26, like Hashem's name, to scare away Mazikim. Moshe changed the order, for it is not proper for His name to be written in order amidst Tum'as Egypt. 1
Moshav Zekenim (22) #2: Hashem in His humility hinted that Yisrael are saved in the merit of Moshe and Aharon (the blood on the Mezuzos below) and Himself (the blood on the Mashkof above). Moshe deviated, for the merit of Hashem must be first.
Tosfos ha'Shalem (22:5): This is difficult. In any case His name is not written. There is merely a hint through the Gematriya!