Two Questions on Parshat Chayyei Sarah

Q: Why did Yitzchak wait until Chayyei Sarah to get married (24:67)?
A: Until then, he wasn't in that parsha.

Q: Why did Avraham marry Keturah all the way at the end of parshat Chayyei Sarah (25:1)?
A: He really wanted to beforehand, but now he didn't have to worry about ruining his kid's shidduchim.

And one for Toledot, for which I have no answer:
Q: Why does the third pasuk (25:21) say that Yitzchak prayed for his wife Nochach (וַיֶּעְתַּר יִצְחָק לַיהוָה לְנֹכַח אִשְׁתּוֹ)? Wasn't his wife named Rivka?