You'll never reach this goal, but you can come close. You want to sell something to the guy who comes in to get a 24 x 1.75 tire for a Schwinn unicycle. You want him to tell his friends that you have everything so they will buy from you too. Do everything yourself that you can. Get your wife to help.
Labor costs are the expense that kills the most businesses.
Read the trade journals and the retail magazines very carefully. The things advertised in Bicycling Magazine are the things your customers will want to see. Most customers want to see the fancy high-ticket stuff, but what they buy is the common everyday replacement parts. Stock just enough of the fancy stuff to draw the people in, like a museum does, but have lots of the common things on hand. You can sleep better knowing your store is protected and your insurance will cost less.