Good luck. I think having a web presence is going to be key, because that's where a whole lot of business is done these days. That's going to be your biggest competitor, and you very well may have a really hard time keeping your prices low enough.
What you can offer that a website can't is a real human who knows what's in stock, which widget to choose, and so forth. Good customer service is getting more and more rare, yet more and more important. The person who walks through that door is your highest priority. I've got nearly ten years of retail experience, so I'm not just making stuff up. I'll pay a bit more if the store is organized and the people nice, helpful, and knowledgeable (without being know-it-alls). Even better if I can also call or email ahead to be sure you have what I need before driving all the way down there.
I've always wanted to open my own store, so I'm slightly envious. I wish you all the luck in the world!