CWP uses WHMCS, but your billing system should not depends a control panel.
Use the system you like more.
First you have to install WHMCS follownig their simple install guide.
After you have it up and running, then follow the guide how to install the CWP Module into WHMCS.
Or is you have Softlacous installed, they have WHMCS there to install also, then again just install the CWP Module afterwards.