Can you explain how I can add additional fields to the 'Edit Appointment' Form? 

Sure.

First define your field(s) in the CCCalAppts file. Next, from the Daily layout on the calendar, run the Show Status Area script and enter layout mode, navigating to the "Mini Window Edit Appointment" layout. Once there, copy one of the existing fields and paste it back on the layout; then double click on this field change it to be one of your newly created fields.

HTH!