In Parshas Vayeitzei, Yakov himself referred to Hashem as "Pachad Yitzchak"; why here does he refer to Him as "Elokei Yitzchak"? And why does he repeat the word "Hashem"?
Rashi: Yakov was referring here to two promises that Hashem made to him; one, when he left his father in Be'er-Sheva on his way to Charan, where Hashem, referring to Himself as "Hashem, the G-d of Avraham your father and the G-d of Yitzchak" promised to protect him wherever he went; the other, just before he left Charan, where, referred to by the Name "Hashem", He ordered him to return home and promised to accompany him (to protect him). In the current Pasuk he is evoking both of these promises - the first half of the Pasuk refers to the first promise (which partially quotes the words of Hashem himself - hence his use of the words "Elokei ... Yitzchak"), 1 the second half, to the second promise, where Hashem mentioned only the Name "Hashem").
Hadar Zekenim (8), Da'as Zekenim (8): Yakov thought that Yitzchak had died. Refer to 32:8:4:4.
Seeing as Yakov's Tefilah begins only in the next Pasuk, what is the significance of this Pasuk?
Seforno: He began his Tefilah with words of praise and Z'chus Avos, just as the Anshei Kenesses ha'Gedolah introduced into the Amidah.
Why did Ya'akov Daven only after he had divided the camp into two and before?
Oznayim la'Torah: Because he was afraid following the newsd of his meesngers, and was not able to concentrate fully until he began to make preparations for the forthcoming encounter and his fear abated.
Hashem said "ve'Eheyeh Imach", not ve'Eitivah Imach"?
Oznayim la'Torah: If Hashem is with a person, that is the best thing that can happen to him.
רש"י: ובבית לבן אמרת לי שוב... ואהיה עמך: קשה שלעיל (לא, ג) פירש רש"י שפסוק זה בא לומר שכשאתה בבית הרשע אין אני עמך?