@mongosapien 

When you mention free-roaming I think you are referring to having a mesh network. You will not have a mesh network, but just multiple network devices that happen to have the same network name so you might see only one network name on your phone for example. What will happen is it will come down to your wireless device to determine what node to connect to, the network devices won't recommend anything, which is what a mesh network does, in that it recommends what node to connect to.

So you can attach the C7 to your main router which will work. To avoid any interference, make sure the wireless channels are running differently. For example, set your main router 2.4G to channel 1, and set the C7 to channel 6, and the other C7 to channel 11.