1)
Why does it say "Ki"?
1.
Radak: This is the reason for the end of the previous verse. They went to his place [confident] in Eli's Brachah [that she will have more children].
2)
What is the meaning of "Im Hashem"?
1.
Radak citing Targum Yonasan: He served in front of Hashem.
2.
Malbim: It was as if he was not Elkanah's son. He was planted in Hashem's house, and sprouted and grew in years and in Chachmah.
