Strong disagree on Chiang wanting to keep the communists around.  He wanted to take care of them before facing the Japanese.  Ultimately both sides tried to send each other into the meat grinder against Japan but the CCP were much more successful than the KMT at guerrilla warfare against each other.

In the 1920's Chiang purged the communists when he found out that the Soviets were trying to take control of Shanghai.  There was no upside whatsoever to having the communists around, which they proved after the war.