What is "Ma'afel"?
Malbim: It is something that covers light. It is not Ofel (darkness).
Why does it say "va'Yavei Alav (singular) Es ha'Yam"?
Rashi citing Shochar Tov: If an Egyptian fled not to enter the sea, a wave chased him and absorbed him [into the sea].
Radak #1: It refers to Pharaoh. Even though he was not mentioned, the Egyptians were mentioned.
Radak #2: It refers to the Egyptians as one entity.
Why does it mention a long time in the Midbar?
Malbim: You did not have full Emunah, and needed 40 years in the Midbar to cleanse you of Tum'as Mitzrayim