1)
Since the word "Eretz" is feminine, why does the Torah say "v'Lo Nasa" (which is masculine)?
1.
Rashi and Seforno: What the Torah really means is that the pasture was insufficient, and the [masculine] word "Mir'eh" (pasture) is self-understood.
2)
Why does the Torah repeat the phrase "v'Lo Yachelu la'Sheves Yachdav"?
1.
Ha'amek Davar: To teach us that it was not just a matter of a lack of space, but rather, one of bad will on the part of Lot. 1
1
He was keen to join up with Avraham - from a distance, but when he came close, it was too much for him.
3)
How can it be that a great land like Eretz Yisrael did not suffice for them?