How did Leah know when Yaakov returned home that evening, to guide him to her tent?
The Gemara (Nidah 31a) refers to this episode to explain the Pasuk, "Yisachar Chamor Garem" (Bereishis 49:14) - (Yisachar is a bony donkey), which can also be translated as 'A donkey caused Yisachar (to be born).' See also Perush Yonasan.
Why did Leah mention the fact that 'she had hired Yaakov... '? Why was it not immodest to talk like that?
Seforno: To reassure Yaakov that she was not encroaching on her sister's rights, seeing as Rachel herself had agreed to allot that night to her. We see from this statement, indeed from the entire episode, that the Avos and the Imahos treated intimacy like Adam and Chavah before the sin - to have children in the service of Hashem and not for personal pleasure. 1 Malbim -if it were due to physical desire, she would be too ashamed to say this!
Ha'amek Davar: Even though it was immodest, this was better than the shame Rachel would feel if Yaakov entered her tent and left.
But see Tosfos ha'Rosh to Horayos 10b. (CS)
Why does the Torah omit the first 'Hei' in "ba'Laylah 'Hu' "?
Ohr ha'Chayim, Malbim: The "Hu" refers to Yaakov, to inform us that he consented. Seforno - this is because he saw how keen Leah was to be with him, and her good motivation. 3
Tosfos ha'Shalem (6): Yaakov would always go the tent over which he saw the Shechinah.
Tosfos ha'Shalem (2): This shows that Leah was not considered 'Chatzufah' (a wife who verbally requests to have Bi'ah, one of the nine Midos of despised relations - Nedarim 20b).
He accepted her wholeheartedly - a large step forward from the 'hatred' that he previously bore her. (EC)
Why does it say "Sachor Secharticha"?
Tosfos ha'Shalem (4): The double expression hints that Yisachar, who was conceived that night, will engage in Torah and receive reward in this world and in the world to come.
Ohr ha'Chayim: I hired you for two matters - to spend the night with me, and to be intimate with me.
Ha'amek Davar: This teaches that Yaakov's intimacy was not for pleasure, Heaven forbid! Rather, he is obligated to his wives. Now he was obligated to Rachel, and Leah acquired this from her.
Why did Leah need to go to greet Yaakov? Did she not trust Rachel to fulfill her word?
Ohr ha'Chayim #1: There was no Kinyan (acquisition) about this. If "Lachen" does not mean a Shevu'ah, she could retract. And even if it means a Shevu'ah, Rachel did not say 'this night,' so she could trade it for another night.
Ohr ha'Chayim: Rachel would fell pain and jealousy if Yaakov entered her tent, and left to be with Leah.
Why was Yisachar born as a result of Duda'im?
Maharal (Chidushei Agados Vol. 3, p. 229, to Sanhedrin 99a): Chazal teach that a wife who asks of her husband for the Mitzvah (i.e. she indicates her desire to him), merits children who will be Talmidei Chachamim, like Yisachar (Eruvin 100b). Leah yearned to be with Yaakov; 1 she gave Duda'im to receive Dodim (her husband's affection), and merited bearing Yisachar. 2
Maharal (Gevuros Hashem Ch. 43, p. 162) - In a wife's yearning for her husband, she attaches her Chomer to a Tzurah (see note below), attaining fulfillment. The Gemara writes that her children will be Nevonim, drawn after their purpose (rather than after materialism). The righteous Jewish women in Mitzrayim acted similarly, and thus brought the Geulah; see Maharal further.
QUESTIONS ON RASHI
Rashi writes: "I have surely hired you (Sachor Secharticha) - I have given Rachel her compensation." Why not explain simply?
Gur Aryeh: Leah had not given Yaakov anything as hire, she had given only to Rachel.