I know absinthe was still a popular drink with the bohemian set in middle Europe well after the turn of the century. Not sure if it was still fashionable into the roaring Twenties though.

There's a book you might dig in relation to those first few questions, The Brothel in Rosenstrasse, by Michael Moorcock. It's set more in the mid-teens, just before WWI, but it covers some related subjects. Good yarn generally speaking too.