1)
Why does it say "Asher Panav Derech ha'Tzafon"?
1.
Vilna Gaon: It is the gate in the north, that when one leaves through it, he faces north.
2.
Malbim: After he stood in the north and measured from wall to wall, he went to measure the northern gate [Radak ? of Ezras Nashim].
2)
What was the measure of the northern gate?
1.
Rashi: It was like the eastern gate, like the coming verse says.