Why does it say "Alu ha'Susim"?
Radak: Horses of Egypt - Nebuchadnetzar's army is coming. See what you can do! Rise against them, like you used to!
Malbim: I command you to mount horses [and go to fight Nebuchadnetzar].
What is the meaning of "v'His'holelu"?
Rashi: It is an expression of foolishness.
Radak: The chariots should do like they used to do. Rechev is a Klal (the singular applies to many), like "Shesh Me'os Rechev Bachur" (Shemos 14:7). His'holelus is the horses moving to and fro and galloping; it looks like Holelus (frivolity) and madness.
Why does it mention Kush, Put and Ludim?
Radak: They came with Egypt.
I command you to go with Egypt. (So implies Malbim - PF.)
Why does it say "Tofsei Dorchei Kashes"?
Radak: Both of these are Samuch [to Kashes], like "Nahar Nachalei Devash v'Chem'ah" (Iyov 20:17), "Chachmei Yo'atzei Pharaoh" (Yeshayah 19:11), "u'Sfunei Temunei Chol" (Devarim 33:19).
