Living in Vienna, I know the places well - the orthodox church is also very nice inside (you need a good camera: it is quite dark in there). The Griechenbeisl is a pricey place, but the food is excellent.
About Augustin: the plaque is not that old (certainly not as old as the building). He became legendary when he was falling down drunk in the gutter at the time when the black plague ravaged Europe, and they went around with carts to collect the dead in the street, to dump them into a big dug-out (which they would later cover with lime and dirt). They also picked up Augustin. In the morning, he woke up surrounded by bodies, crawled out and went home. It is believed that the alcohol saved his live, at least the Viennese, with their fondness for wine, think so.
Which reminds me of this old joke: The teacher tries to demonstrate how bad alcohol is. He filled one glass with water, another with alcohol. Then he dropped a worm into each glass. The worm in the water glass swam happily around, but the worm in alcohol died and sank to the bottom. Then the teacher asked: "What can we learn from this?" - Little Maxi stands up and says: "Drink plenty of alcohol and you won't get any worms!"

Correction about the "Madonna" - not Mary Magdalene - the mother of Jesus was Mary: https://en.wikipedia.org/wiki/Mary,_mother_of_Jesus
Mary Magdalene was a follower of Jesus https://en.wikipedia.org/wiki/Mary_Magdalene
two different persons.