There used to be a comic/game shop not too far from me. The owner sold comics, cards, game stuff, and even Warhammer stuff. My friends and I would go there on Friday nights to play D&D. It was a nice place, very big. I think it was too big though, as he eventually had to close his store and he and his wife moved. I also think part of the problem was that he hadn't advertised around enough and he would take a bunch of warhammer stuff off the shelf and paint it himself to display. I understand the need for a display, but I don't think it's necessary to take hundreds if not thousands of dollars off the shelf for a display.
In any case, I'd say to start a gaming store you should definitely start small to keep the overhead low, and expand as necessary.
