Why did Avraham opt to attack them at night-time?
Seforno: This was a clever strategy, to trick the kings into believing that there were more soldiers than there really were. 1
What does the Torah mean when it writes that the night split up on them"?
Rashi #1: It was not the night that split up, but his army, in order to pursue the fleeing segments of the enemy, in the way that armies tend to do.
Ramban: Avraham chased after them by day as far as Dan; then, at night, when he did not know which way they would flee, he split up his army into two or three groups to pursue them following all the possible routes that they might take.
Rashi #2: It was the night that split up, the first half for the current miracles, whilst the second half was reserved for the miracle of Makas Bechoros in Egypt.
Seforno: Avraham split his army into two, leading them to believe that they were being attacked by the surrounding armies. 1
How could Avraham have pursued the kings up to "Chovah", when no such place exists?
Rashi and Targum Yonasan: 'Chovah' is a synonym for sin, and it refers to the image that was later set up in Dan (mentioned earlier). 1
It says "he struck them and chased them" - does one chase the dead?!
Da'as Zekenim, citing Midrash Tanchuma: Avraham chased and Hashem struck.
רש"י: ומדרש...שנחלק הלילה: מנין לדרוש כך?
גור אריה: לא כתוב 'ויחלק אברם ועבדיו עליהם לילה' אלא "ויחלק עליהם לילה", משמע שהלילה עצמו נחלק.