Hello Sir and Welcome to the Cayenne Community,
You can add whatever number of devices you want to your Cayenne Dashboard.
The system will behave as follows: You will see all the connected devices on the left side of the Dashboard, and when you click some of the device, you will see the widgets that are related to this device, BUT if you want to combine a dashboard with a widgets from different devices (no matter how many or what type of) you can make a new project with the plus sign on the top of the window. There you can add the different widgets from the devices that you want.
If you have any questions regarding this functionality of the platform, do not hesitate to ask