To answer your questions:
1. In the Location settings, you can choose whether or not the Client Admin receives an email on all ticket updates (Setup -> Locations). Enable that option for the Location and the Client Admin that is assigned to that Location will receive an email upon any ticket update.
2. The tech will receive an email upon any ticket update if you enable that option for each tech (Setup -> Techs -> choose a Tech -> Email setup section, look for Notifications options)
I currently have our Help Desk configured in such a way that the assigned tech receives an email upon any update to the ticket. We don't, however, send emails to our clients when a ticket has been Closed, but I have experimented with that before. If my answers are not satisfactory, then I may have misunderstood your question, so please clarify if this is the case.