The Offline mode was added to Bidule so that it could be used to
You cannot use an audio device (input or output) in Offline mode. In almost all cases, you will use an Audio File Recorder bidule (or more than one) instead to record the offline output.
When using the Offline mode, you will notice that the standard cpu gauge has been replaced by an elapsed time meter, which should give you an estimate of the speed at which the render is done.
The ReWire Devices configuration dialog lets you specify defaults number of MIDI inputs/outputs, number of audio outputs and if the ReWire application should be launch/closed automatically. Use this to set up as many MIDI inputs you want for a ReWire device or restrain the number of audio outputs to only 2 if you only want to have the master output. If you have multiple layouts using ReWire devices and you want to be able to quickly change between them, make sure to un-check the auto-launch option, this will keep the ReWire application opened and it will be ready to use as soon as the layout is loaded.