@GeneG 

You will only ever need one powerline adapter wired to the router which you already have so you are good on that end.

When you get your wireless adapter kit plug each one into an outlet and see if the powerline light comes on, if so do not need to pair it. If the light is off, then you would hit the pair button on a powerline adapter currently working, and then hit the pair button on the new device.

You can look at the TL-WPA4220 KIT or the TL-WPA7510 KIT. The powerline network will set to the speed of the slowest powerline adapter on the network so if you get a TL-WPA8630 KIT AV1300 the entire AV speed will go down to AV500.

Good morning, Tony, and thanks. I had believed that all I had to do was plug in (and possibly pair) the new units, but I wasn't certain after reading all the info on extending the system. Thank you for clearing up that confusion!