each set is already "synch'd" with each other and just requires a simple button press to join them. However I have heard that you can buy extra satellites soon and once you do, all you would have to do is hit the sync button on them and confirm the M.A.C address with the control panel for the main router. I will tell you from experience with "repeaters" that once they are connected it will give you wifi and it will be decent, but the speed will be cut in half of that of the main unit. That is just how it works in the real world. However since the wifi is quite fast and has large area of coverage you will most likely not notice that difference from a older router speed .
My wifi is running at 850Mbs and satellite runs around 500 Mbs, but since my older router was only pushing 300-400Mbs I did not really care since on that end of the house it was just tablets, phone and such that were maxed out on speed anyway