Great idea. One question:

Are you going to use your own collection to start? If not where is the product going to come from?

I really think you should have games/items from as many systems as you can. For me, this is what makes a game store good. This alone will not be enough, though.

For example:
There is an AWESOME game store two blocks from my house. They have top loaders, sega CDXs, rare games of all sorts, but they are way overpriced, so I never go there. It is a real shame to have such a wonderful inventory, but to have it worthless to me.

My fav store in town is called "Cool Stuff." They sell music, movies, and games. They are fair, honnest, and knowledgeable. They price their games at 75% of DP listing, which I think is fair.

All in all, I think you will do great as long as you dont get greedy, stingy, or rude.

Good luck,
-james