What is the significance of the fact that the Torah places Yishmael before Yitzchak?
Ramban (citing the Midrash): We see here how the son of the maidservant gave Kavod to the son of the main wife.
Why did the Bnei Keturah not participate in the burial of their father?
Malbim (6): It is because Avraham had sent them far away (verse 6). Oznayim la'Torah
Why does it say "El Me'aras", and not b'Me'aras?
Refer to 23:19:154:1 and the note there.