1) Can't really comment on that as a typical event manager has several different tables with very different numbers of records in each table so it would depend on the design of your tables and relationships.
2) Ditto #1
The typical relationships found in many report managers look like this:
Each Record in Event_Contact links one contact to one event. A contact can participate in multiple events and an event can list multiple contacts (which can be employees, vendors, performers, guests....) 1) would appear to describe counting the records in Event_Contact for a given event, but that does not require any kind of self join. 2) would seem to refer to an email address field defined in Contacts. From Events, a count function could count on this email field and provide a count of how many contacts linked to the current event have an email address recorded.