#1 and #2 are commonly caused by the way the join (or lack of join) between tables.
Right click the join line between event and client junction table and select to show all records from the event table and matching records from the client junction table. Do the same thing between the event and the employee junction table.
#3 Your query can reference a combobox or a text field from the form which kicks off the report. This reference would be put in the criteria row of the query.