Not to feed the flames of your sleep deprived insanity, but it is not as unrealistic as you think. I've seen stores that basically only sell Warhammer and somehow still manage to go around.
The place where I buy my books sell comics, manga, anime, genre fiction books (in english), boardgames, role playing stuff and other miscellaneous nerd stuff. It doesnt make enough money to support one shop, but 3.
So it is not unrealistic at all, just very, very hard.