Evaluating - Category / Patient

I am evaluating whether Calendar will work for my purpose as and 'Appointment Book/Calendar'. A primary need is to be able to input a patient's name into the Calendar and be able to select the patient from the lookup/dropdown. The online demo illustrates 'Category' lookup field. Can the calendar template be modified to add an additional lookup field for patient? If not, could the existing Category field be renamed 'Patient'; and is their any limitation on the number of records that can be added to the underlying table?
Doug Perkinson