Thanks for posting that, Bill. I've wondered (vaguely, I admit) how to make that work. Toyota should add another button to the display, whose effect would be to (a) save current settings, (b) impose the required settings for vented non-A/C'd air, then (c) when pressed again restores the saved settings.
Don't thinkl so, unless the petrol engine is too cold. Most of it ought to be done by waste heat. I've not tried what happens if one just gets into a cold Prius and switches on cabin heat. But the car does seem to warm quite quickly, so maybe it has an electrical heater in there, somewhere. Possibly the electrical parts (motor and switchgear) produce useful heat?