Do I Have to Enter Each Customer, Vendor, and Inventory Item Once at a Time?

No!  You can save hours of manual data entry by importing your company information from QuickBooks Financial software or from Microsoft® Excel (commercial license). QuickBooks Point of Sale imports data from any QuickBooks Pro or Premier Edition 2008-2012, QuickBooks Enterprise Solutions 8.0-12.0, or Microsoft Excel (Commercial License) 2000, 2002, 2003, 2007, or 2010.  Note: These applications are sold separately. 

Microsoft Office Home & Business or Professional contains Microsoft Excel with a commercial license for use with importing items into POS.