1)
Why did Hashem promise Hagar that He will make Yishmael a "great nation" (Goy Gadol), whereas He promised Avraham (earlier, in Pasuk 13) only that He would make Yishmael into a nation (le'Goy)?
1.
Hashem promised Avraham as well that Yishmael would be a 'great nation' (Goy Gadol), before Yitzchak was born, so it was not necessary to repeat that to Avraham. Hashem emphasized here to Hagar that Yishmael will be a great nation since Avraham only told her the more recent prophesy about her child, that he will be a nation (without the word great) (MK)