I am not an expert of this topic but i also thought of setting up a shop also selling online.
Here are my thoughts or ideas … Rent a shop however small it may be and specialize in items that are not available in regular Computer sales shops.
I am assuming that you are following the latest tech so you can get the latest tech to your consumers.
Maintain DVD of latest version of all major Linux distros .
You can also specialize in high powered Rigs . Because i often see my friends buy whatever the seller says to buy and end up with a low power rig at almost the same cost of a good one which can do nothing.
You can also maintain few entry level IEM & headphones .