The answer to that depends on so many factors it would be impossible to tell. Even if you went live with the most awesome site and to die for designs without "aging" and any marketing to get traffic there your initial sales will be low to nonexistent. I sell CafePress shirts and some of my own rhinestone apparel. I sell very few apparel via my own site, and CP sales are plentiful. However I have had my CP shops for well over a year and my rhinestone apparel is only 6 months old. When I vend at horse shows, the sales are seasonal, if its cold everyone wants a sweatshirt and when it is warm the T-shirts are appealing. You need to get people to your store however in order to sell anything

I am sure others will have more input as well.