Congratulations RM, that is AWESOME!

Based on my own gripes with bike shops I'd say: don't stock the earth, but have catalogues easily available for browsing and be willing to order. Be scrupulous about notifying your customers whenever whatsit comes in!!! I love it when my lbs manages to send me a text message. Which is about half the time..

Recognize that some commuters (like me) can have a (slightly pathetic) addiction to their "work horses". If you promise to fix x,y or z in the course of the work day, they (I) can get very antsy if that doesn't happen...
But maybe you're not planning on mechanics.

I agree on stocking everything a biker needs fast. And that interesting clothing is a great way to get people to hang around and browse. Good luck! How exciting!