What is the significance of the Name Keil Shakai that the Pasuk uses here?
Rashi: It means 'the G-d who possesses all the means' - in this case to fulfill the blessing that He confers upon whomever He blesses. 1
Ha'amek Davar: HaSh-m said "Dai" - the world is [big] enough for the revelation of His honor, which is the purpose of creation. HaSh-m will later appear to Yaakov with this name (35:11), for it will be fulfilled through him.
What exactly is the difference between "Yevarech," "Yafrecha" and "Yarbecha"?
Seforno: HaSh-m promised to bless him with money, children and greatness, respectively. 1
This corresponds to the three Berachos that HaSh-m conferred upon Avraham (12:2).
What is "Kahal Amim"?
Ha'amek Davar: "Kahal" is 10 (Kesuvos 7b); "Amim" are nations with different lifestyles, even if they are under the same kingdom. 1 Yaakov will be 10 Amim; almost every Shevet had its own customs. Only Binyamin and Yehudah were the same, and Efrayim and Menasheh were the same. Levi is among the others. 2
Ha'amek Davar: Men and women are called two Amim (Shabbos 62a).
He did not bring a source. Perhaps this is why Binyamin chose to stay with Yehudah when Yarav'am started Malchus Yisrael. However, Levi was very different. They do not farm the land; Yisrael supports them for their Avodah and Torah ("Yoru Mishpatecha... l'Yisrael" - Devarim 33:10), they were counted separately, they alone came to kill Ovdei ha'Egel (Shemos 32:26), and fought Yisrael who began returning to Egypt after Aharon died (refer to Bamidbar 26:13:2:1*), Kohanim are called quarrelsome (Hoshe'a 4:4), and prone to be very irritated (Bava Basra 160b)! Do not say that Levi lived among the others and were not recognized as a separate Am. They had their own cities. Also Shimon lived among others, and they count as an Am! (PF)