You either connect a mic via Bluetooth or wired headset.

From my experience, its overall good. Its basically stock android, meaning no google smart features and apps by default, with more control over apps and google services. But for caution, some apps may break. You will have to mess around with the app settings to fix them. Also some apps will not work such as the google wallet app due to the OS not being acknowledged as official by google.

In short, its a more security focused OS that may require more involvement in configuration.

No it’s a local application like Libre. Can also be ran in the cloud.