Why does it say "va'Yhi Acharei Chen"?
Malbim: This teaches that one Aveirah leads to another. (Because he went to a Zonah, he later married Delilah, through whom he would stumble.)
What is the significance of the name "Nachal Shorek"?
Bamidbar Rabah 9:24: There he became like a Serak (barren) tree, that does not make fruits.
Why does it mention her name? It did not mention the name of his first wife!
Malbim: His first wife, he converted her and changed her name to a Jewish name. Delilah did not convert, and kept her name. In Timnah there was [Halachic] marriage, but not in Azah (Yerushalmi Sotah 1:8). Chazal expounded her name (Sotah 9b) - [due to her], Dildelah (became poor) his strength, deeds and heart.