No, you don’t need your own AudioDeviceManager instance or an AudioIODeviceCallback, the standalone application part in the plugin template deals with all that, you only need to implement the AudioProcessor subclass like you would for a plugin. The downside is that if you need to customize how the standalone application looks like and behaves, that is not very well explained anywhere.
If you decide to have your own custom standalone application with an AudioDeviceManager and an AudioIODeviceCallback, the corresponding methods are :
AudioProcessor::prepareToPlay : AudioIODeviceCallback::audioDeviceAboutToStart
AudioProcessor::releaseResources : AudioDeviceIOCallback::audioDeviceStopped
AudioProcessor::processBlock : AudioIODeviceCallback:: audioDeviceIOCallback
For the processBlock call you have to form an appropriate AudioBuffer from the arguments passed into the audioDeviceIOCallback method.