How is the Thermomix Friend® connected to the TM5?  

The Thermomix® TM5 cannot connect/pair to the Thermomix Friend®, since TM5 does not have Bluetooth®® capability. The Thermomix Friend® is compatible with the TM5, but the cooking steps must be entered manually on the Thermomix Friend®. Simply read the setting instructions in the guided cooking steps and set the Thermomix Friend® manually to start cooking. 

Do I need the Cook-Key to be connected to my Thermomix®TM5 as using the THERMOMIX FRIEND®?

As the cooking steps are manually set on the THERMOMIX FRIEND® when using the TM5, you can set the steps on TM5 for combined recipes manual on the TM5 as well. But of course, you need an active Cookidoo account to have access to these recipes. Without cook-key they will not be synchronized to the TM5 to perform guided cooking on screen.