You will need at least one Puck to act as a communication hub for your Flair system. We call this the Gateway Puck. It's plugged into power using the supplied cable and adapter, and during Setup you connect it to your home WiFI.
For any room where you install Flair Smart Vents, you'll need a temperature sensor. This can be a Flair Puck, an ecobee/Honeywell smart thermostat, or their remote sensors. So, if you want to use existing remote sensors, get at least one Puck to be the Gateway Puck - and have it centrally located so all the Smart Vents can communicate with it.