What made Rivkah think that Yitzchak was coming to meet them?
Seforno (63): Eliezer and Rivkah were traveling from east to west (from Charan to the south of Eretz Kena'an), whilst Yitzchak was traveling in a southerly direction. Consequently, when he turned towards the east to go home, it looked as if he was now making his way towards them. 1
Why did Rivkah enquire about Yitzchak? Did she ask after every man that she saw?
Rashbam: She asked because he changed direction and began coming towards them. 1
Refer to 24:64:1:1 and the note there.
Why did Rivkah add the 'Lamed' in "ha'Lazeh"?
Rashi (in Shmuel 1, 14:1): Because it refers to someone who was standing opposite her at whom she pointed at with her finger.
Why did she cover her [face] with a veil?
Ha'Emek Davar: It was amidst shame. She realized that she was not worthy to be his wife (refer to 24:64:1:7 and the note there).