Why does the Torah see fit to mention that Avraham got up "me'Al Pnei Meso" to speak to the Bnei Ches?
Seforno: Since Sarah was not yet buried, he was [an Onen, and] not an Aveil, and was therefore permitted to go and speak to the Bnei Ches.
Rabeinu Bachye: We learn from Avraham that when a person speaks to a public he should stand up. 1
Hadar Zekenim: He wanted to position himself so he could bow to all of them at once.
Ohr ha'Chayim: This hints that a Mes knows what is said in front of it, until the coffin is sealed (Shabbos 152b), and hints to the custom to bury a Mes lying on its back.
The Torah records again (in Pasuk 7) that he stood up before speaking to the Bnei Ches.
Why does it say va'Ydaber and also Leimor?
Ohr ha'Chayim: He requested a burial place, which implies any place. "Tenu" implies a free gift. He clarified that he wants specifically Efron's field, and that he does not want a gift.
Why does it say va'Yakam, and also va'Ya'amod?
Ha'Emek Davar: It was hard to leave his Mes and the eulogy; he got up with zealousness.