1)
What is "ba'Derech Asher Tishlachem"?
1.
Radak: This is like "va'Yhi Devar Shmuel l'Chol Yisrael" (Shmuel I, 4:1), and when they asked from the Urim v'Tumim, like in the war against Binyamin (Shoftim 20:18, 23), and similarly when there will not be a punishment on them.
2.
Malbim: When they merit, they will go to fight the enemy outside Yerushalayim, in Eretz Yisrael.
2)
What is praying "Derech ha'Ir"?
1.
Rashi: They face Yerushalayim.
