What you describe in terms of the design work needed to make it happen is not really "basic". It's pretty sophisticated.
First thing is to set up a data model that supports what you want to do. You describe a table for sites and a table for site admissions. Your popover, however shows aggregate data calculated from multiple admissions and discharges. What does one record in Site Admissions represent?
Shouldn't you have a Patients table with one record for each patient?