Why did Yaakov sacrifice specifically to "the G-d of his father Yitzchak" (See Sifsei Chachamim)?
Rashi: Because a person is obligated first and foremost to honor his father (more than his grandfather). 1
Ramban: Yaakov knew that his descent down to Egypt was the beginning of Galus Mitzrayim for him and his children. Afraid that the Midas ha'Din 2 (the symbol of his father Yitzchak - Pachad Yitzchak), was laid out before him, he brought sacrifices to mollify it. 3
Rashbam: He was following in the footsteps of his father, who had built a Mizbe'ach in Be'er Sheva and brought Korbanos on it. 6
Malbim: (a) Yitzchak built a Mizbe'ach and went to offer there. (b) Hashem had told Yitzchak not to go down to Egypt - therefore Yaakov did not intend to settle in Egypt.
Ha'amek Davar: Yitzchak had special Hashgachah regarding income. It says here "Elokei Yitzchak" for this reason, even though in Parshas ha'Korbanos, it never says 'Kel' or 'Elokim,' only 'Hashem' (Menachos 110a)!
Ramban, Moshav Zekenim: It could have said 'lEi'lokei Avosav,' without names! Also, when Yaakov prayed on a different occasion, he put Avraham first -"Elokei Avi Avraham, vEi'lokei Avi Yitzchak" (32:10)! Refer to 46:1:1.1:1.
Ramban: Hence his use of the Name 'Elokim,' even though we generally find that the Name 'Hashem' is used in connection with Korbanos.
Ramban: That is why Hashem responded with the Name Elokim and calling Himself "Elokei Avicha" (46:3), allaying his fears, and instructing him to go down to Egypt, where his family was destined to thrive, despite the Shibud that was about to begin.
See 26:2.
And here he was doing the very same thing! So he brought Korbanos as an atonement.
See 26:25.
Why did Yaakov offer Zevachim (i.e. Shelamim), seeing as Avraham brought Olos (as is the way of the Bnei Noach)?
Ramban: To make Shalom among the Midos. 1
Ha'amek Davar: Shelamim are appeasement for the sake of income (Parnasah). Yaakov did not offer Shelamim while he was mourning over Yosef, for then he was Chaser (lacking). Now, his spirit returned.
As the Midrash, commenting on the name 'Shelamim,' explains - because they bring peace to the world.
Why did Yaakov offer Korbanos in Be'er Sheva?
Ramban: Because it was the location of prayer of his fathers. That is where he went to seek permission to go to Charan. 1
Rashbam: Refer to 46:1:1:4.
Ha'amek Davar: He thought to move from Chevron to Be'er-Sheva, where his father found "Me'ah She'arim" (i.e. great success - refer to 26:12:2) at a time of famine.
See Ramban to 28:10.
Here it says that Yaakov traveled. Why does it say only below (46:5) that his children carried him in the wagons?
Malbim (to 46:1,5): Initially, Yaakov did not agree to uproot his residence. He intended only to go to see Yosef, and return - "I will go and see him" (45:28) - and no more. He did not use the wagons, for they were sent on condition that he travel with intent to settle permanently. After his Nevu'ah (46:2-4), he intended to settle there, so he used them.
Ha'amek Davar (to 46:1,5): Now he had the high spirit of Yisrael; his children did not need to carry him. After he knew that he is going to exile, his spirit was lowered, and he could not go by himself; they needed to carry him.
QUESTIONS ON RASHI
Rashi writes: "'To the G-d of his father Yitzchak' - A person is obligated to honor his father, more so than his grandfather." Ramban asks - Let the verse include both, by writing 'the G-d of his forefathers'! Additionally, when Yaakov prayed before his encounter with Esav, he did mention Avraham before Yitzchak (32:10)?
Gur Aryeh: On this occasion. Yaakov offered Korbanos, which bring a person close, connecting him with Hashem. It was therefore fitting to invoke Hashem's relationship with Yitzchak, "Pachad Yitzchak" (31:42). 1 In prayer, however, he was invoking his forefathers' merit, and so Avraham is mentioned first, in order.