Contacts can be uploaded per location on the website. Simply select a Location, click "Upload Contacts", and build your contact list using the provided template. The form will allow you to upload the list and provide record by record results. When you need to make changes to a location's contacts, simply upload a new list to overwrite the previous. (Keep the contacts file in a safe place, as you will modify this file if you need to update the contacts)
Once the contacts are uploaded to the location, they will automatically be available to all the iPads linked under that location. Using the Custom Forms on the Secret Settings page, add a new field type "Contact Lookup" to begin using the Contact feature in the app.