1)
How will Kasdim be "l'Shalal"?
1.
Radak #1, Targum Yonasan: Eretz Kasdim [will be plundered].
2.
Radak #2: The congregation of Kasdim [will be plundered].
3.
Malbim: After Bavel (the capitol) is defeated, Kasdim (the rest of the country) will not fight. They will be like booty that remains (for the victor to take) after the war.
2)
Why does it say "Kol Sholeleha Yisba'u"?
1.
Malbim: When one conquers a land after many wars, the loser hides all their property, or destroys it, lest the victor get it. Here, the victor will find more than it needs.