Do I need additional license to use CMS? (How to compute license for CMS)

Yes.

Each NVR connection is similar to one IP camera connection. Therefore for each NVR connection you need additional one channel license. Only professional edition and intelligent edition qualifies the use of CMS.

Let's use an example scenario in the following diagram. A primary NVR server connects to 2 child NVR servers, which individually has two IP cameras connected. The small blue box highlights the license requirements. This example requires 6-channel license installed in a way that Primary NVR server has two channels, NVR server 1 has two channels, and NVR server 2 also has two channels.