"The Complete Idiot's Guide to Starting an Online Business" by Frank Fiore and "How to Start and Operate a Mail Order Business" by Julian L. Simon.
Also look for organizations like the National Mail Order Association to help you 'fill in the blanks' as you start your business. These organizations are there to help people enter their industries. They can give you some guidelines as to how to go about managing inventory or make recommendations to drop-shipping services if you chose not to hold inventory.
Good luck on your new business,