The Cisco rebranded ARC consoles only support getting directory info from CUCM via AXL. Arc does offer two additional consoles (not through Cisco), that have additional capabilities that can lash into other things like databases.
With the Cisco product, you're limited to adding the external folks into AD, or adding them as speeddials on the console. There are advantages and disadvantages to both.
My understanding is that you simply by the console/user licenses.
The installation comes with SQL 2008 Express version, but depending on how you scale it, you *may* need to upgrade this to SQL2008 Standard or above. You have to bring your own operating system and platform to run it on.