What is the comparison to sand?
Radak: I would bless you with children [numerous] like sand.
Malbim: The adults will be numerous like sand of the sea.
What are "ki'Me'osav"?
Rashi: [Your seed] will be numerous, like fish of the sea. Radak - the matter is repeated in different words.
Radak #1: Me'osav are sand pebbles. They are like Ma'os (coins) that Chazal discussed.
Radak #2: Like the innards of the sea, i.e. fish.
Radak citing Targum Yonasan: They are sand pebbles, like small grains.
What is "Shmo"?
Radak: It is [your] seed. Even though you did not hearken to My Mitzvos, I will not totally cut you off. Rather, I will exile you to the land of your enemies, and afterwards I will redeem you, and tell you "leave Bavel" (20). It says "Shmo" in place of Zar'echa, for most of the captives in Bavel were the children; their parents [who were exiled from Eretz Yisrael] died.
Why does it say "mi'Lefanai"?
Radak: I will not return you in front of Me in the Bayis of My Shechinah.