Mike,
Some people think that having both management port and dataport is mandatory or best-practice.
Unless you have a specific need for it, I would go for just the management port and leave data unconfigured. Reason for that is that having two ports complicates the deployment. Please read the Technote on ClearPass Service Routing if you want to understand the feature. If you don't understand or are unsure, deploy ClearPass on a single interface.
To skip data port configuration during the initial setup, just press Enter on the question for the IP address of the data port. If you already configured the data port IP, remove the values in the server manager.