1)
Why is the Nevu'ah directed first at Pharaoh, and afterwards at all of Egypt?
1.
Malbim: Pharaoh made himself (claimed to be) a god, and he ruled strongly, and his fall was the fall of the entire nation.
2)
Why does it say "v'Al Mitzrayim Kulah" (feminine)?
1.
Radak: This refers to the Edah (congregation).