Auto create related records

[TraciAnn via AccessMonster.com]

My db tracks activities that are scheduled to occur for a given project. The
activities need to be dynamic, allowing managers to add and remove activities
at will during the course of the project. At the beginning of the project
(and throughout), contacts are assigned to the project and need to have a
record created for each activity within that project. As the project
progresses, a DateStamp and UserStamp field is populated by a db user,
signifying the contact completed the said Activity.

Structure:
Project table
ProjectID (PK)
Project

Activity table
ActivityID (PK)
Activity
ProjectID (FK)
Sequence (Order in which activities are to be completed)

Contact table
ContactID (PK)
ContactFirstName
ContactLastName
etc.

ProjectContact table
ProjectContactID (PK)
ProjectID (FK)
ContactID (FK)
Role

ContactActivity table
ContactActivityID (PK)
ContactID (FK)
ActivityID (FK)
Completed (Y/N)
TimeStamp
UserStamp

Needed:
1. When a record is created in ProjectContact, how can I automatically create
ContactActivity records for all the activities associated with the same
project?
2. If a manager adds an Activity record to the project, how do I
systematically create ContactActivity records for Contacts already assigned
to the project?
3. Are there other issues I need to consider in this process?

Thanks for all your help guys! You are WONDERFUL!!!