What is the significance of the fact that Avraham died 'satiated'?
Seforno: He saw and achieved everything that he wanted to.
Ramban: He lived a life of satiation, inasmuch as there was nothing that he did not have that he desired. 1
Targum Yonasan: He saw Yishmael do Teshuvah in his lifetime. 2
Rashbam: The suffering that was destined to overtake his children did not begin in his lifetime, because he lived a peaceful life and died in peace. 3
As the Mishnah says in Pirkei Avos 'A rich man is one who is satisfied with what he has'. Indeed, the Pasuk uses virtually the same expression in connection with Yitzchak (35:29) and David ha'Melech (in Divrei ha'Yamim 1, 29:28).
What does "Va'ye'asef el Amav" mean?
Seforno: It means that he went to join the other Tzadikim in Olam ha'Ba - "Amav" in the plural, because each Tzadik has his own personal Chupah there. 1
Malbim: The Nefesh goes to its 'nation' and the place of its 'birth'
As the Gemara says in Bava Basra 75a 'Each and every Tzadik is singed by his friend's Chupah' (because he knows that he could have acquired the attribute for which his friend received his Chupah).
What is the difference between va'Yigva and va'Yamas?
Malbim: Gevi'ah is cessation of bodily powers. Misah is separation of the Nefesh from the body. Gevi'ah and Asifah are said only regarding Tzadikim, who are gathered to a spiritual domain.