Model name reported by the device, or null when nothing is connected.
How the connected device is attached, or null when nothing is connected. Worth saying out loud in the UI: the two differ enough in responsiveness that a reader on a slow display should be able to see which one they got.
Layout of the connected device, or null when nothing is connected.
Why the last attempt failed, for display next to the connect control. Empty when there is nothing to report.
Connection state, plus what to tell the user about it.