Abstraction-
I agree with not stocking 3e materials. But, I wouldn't expect 4e to be a big enough splash to justify delaying opening your shop.
IF your area has enough room for a(nother) gaming store, then you might as well open now. I would counsel caution, though.
Consider seriously what you intend to accomplish. Do you intend for this store to be your full time job? Or do you intend for the store to break even, maybe make a couple of bucks, and to be something you do as a second job?
Consider seriously what competition is in your area. What do they mostly sell? Is there some niche they're neglecting?
Consider seriously who your target market will be. A store which appeals primarily to miniature wargamers will not necessarily get the kids in the door to buy collectibles, for example.
If you expect to sell to the Yu-Gi-Oh crowd (and there's nothing wrong with courting that crowed), consider seriously whether you can afford to invest the money in making your store family friendly. Consider whether you can invest enough of your personal time to make the store family friendly. A family friendly store needs to not make parents nervous when they leave their kid there. It needs trustworthy looking adults, a clean atmosphere, nice lighting, and so on.
Consider whether you can afford the space for tables. You can't sell extras like food and drink if you don't have tables for people to play.
Consider whether you can invest the time and money necessary to sell your product. Something like an official game night for kids and families can be a great way to move boardgames, for example. Can you dedicate a regular weekend once or twice a month to this? Can you afford to use your own inventory to demo games, knowing that any game you open to demo will be unsellable?
Can you invest the time necessary to make sure that coming to your store, or purchasing games through you, is more pleasant than doing it online?
Do you know enough about business to run the place? Have you considered courses in small business ownership, and retail?
I'm not trying to discourage you. I'm just trying to put some of the realities out there.
My area has three gaming stores in a half hour's drive from most of the bedroom communities.
One is a pretty professional looking store that sells primarily to the collectible card gaming / collectible miniature gaming community. Its bright, well lit, has good, clean carpet, good clean lighting, and is in a respectable plaza. It runs regular tournaments for kids, and has a small crowd in it most nights and weekends. Its also a full time job for its owner, and even with this success, I doubt he's rolling in cash. This store does not sell miniatures, and moves very few books or boardgames.
A second store focuses heavily on boardgames and gaming books, with only a side business in collectible card games, and barely any collectible miniatures. Its bright and clean, and has a "game day" every other month, which is like a little miniature store wide convention. Its employees are on hand constantly, doubled up, so that if you want to learn a new game, someone is available to play it with you. Its in a decent but not amazing plaza. What makes this store tick? Mostly the fact that its employees are pseudo volunteers, none of whom works there full time. I believe the owner is the same.
Finally, there's a store that caters to miniature wargamers. Its the only store where you can find a full wall of Games Workshop or Privateer Press stuff. It barely has books or board games at all, doesn't carry collectible card games, and mostly neglects the collectible miniature games. It isn't particularly clean, and only after being open a year did they upgrade from carpet samples to an actual carpet. Its in a lousy area, and honestly, I wouldn't want to leave kids there. But this store works because wargamers don't mind these things, and because its owners and employees all have other jobs and don't particularly care how much money they make. They operate the place on a "break even and we're happy" philosophy.
I figured I'd give you this information as a sort of comparison. Of three stores, only one has an owner who works full time. Only one pays his employees "real" wages. One is run like a hobby and makes no meaningful profit, and one exists in a sort of neutral zone between those extremes.
Decide what your goals are, and maybe opening a store is for you. But think about it seriously. There used to be five gaming stores in my area. Now there are three.