You'll probably be surprised to hear that there aren't many books on the actual tactics used by the Viet Cong during the Vietnam War. Few military historians in the west actually use Vietnamese sources which means that they mostly rely on contemporary American reports and studies made during the war itself (or on translated works). You'll also be surprised that the two statements that to you seem like a logical continuation (VC's use of environment -> US adapts strategy accordingly) was not actually a reality in the Vietnam War. Tactically, however, there were some adaptations.

A good place to start reading about VC tactics for a beginner is Inside the VC and the NVA by Michael Lee Lanning & Dan Cragg (Texas A & M University Press, 2008) which is a more general book on the VC and the PAVN (People's Army of Vietnam). It does contain plenty of valuable information on tactics and use of environment by both the VC and the PAVN.