1)
Why does it say "Es Amud he'Anan"?
1.
Ibn Ezra: Normally, "Es" just before the object [on which the subject acts]. Here, Es is just before the subject - the cloud, which did not veer from them. This is rare; other examples are "v'Es Malkeinu... Lo Asu Sorasecha", "u'Va ha'Ari v'Es ha'Dov."
2)
What is the meaning of "beha'Derech"?
1.
Rashi: This is like ba'Derech (on the way).
