1)
Why did he say to fight only Melech Yisrael?
1.
'Rashi' (16), Malbim (Melachim I, 22:31): He had spies, and he heard the Navi's words [that only Achav will die].
2.
Radak (Melachim I, 22:31): If they will fight with the rest of the nation, if Melech Yisrael sees that the war is severe, he will escape. Rather, first fight only the king until you kill him, and afterwards the rest of the nation.
