I have done this for a system with four CUC nodes and two clusters. With regards to ports the part numbers would be "UNITYCN7-ADD-MXPT" and "UNITYCN7-HA-MX". Basically, this gives you a 144 port system with High Availability. In the first port number "MXPT" means "Add Maximum Ports". The second part number "HA-MX" means High Avilability with maximum ports. Presently, maximum ports implies 144 ports.
As far as what you provision on the system you would have 144 ports licenses for your primary CUC node and 144 ports licensed for your secondary CUC node. A CUC cluster operates in an active-active fashion. Which means, depending on your telephony integration, your cluster can handle 288 concurrent calls (including MWI, outgoing, incoming, etc.). The max capacity is determined by things like the telephony integration you are planning to host on CUC and whether you are doing integrated messaging or not.
I believe the CUWL licensing comes into play with respect to the number of users licenses on CUC. Meaning, this should be included in your CUWL package (assuming Standard or Pro) and you shouldn't have to pay additional money for CUC user licenses.
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