@SJAMISON 

When you get another kit you would place those two units where you need them. Only one powerline adapter is needed to be wired to the router for the rest of the units.

So in your case place one of the adapters where you need it for the new camera, the second unit can be stored in case you need another connection.

I have it set up like this already - one powerline adapter is next to the router and plugs into one of its 5 ports. the other two powerline adapters are connected to a camera in the garage and a camera over the front door under the awning. I think the max is 15 all in the same house power lines. All the powerline adapters make one network together, so you only need one connected to the router and then all the others will communicate through that one.