Hello Jeremy!
Note - my experience is on pre-3.9.. Also I don't know if your scenario involves Sponsor confimation, so just add more information if the answers below isn't sufficient.
Account-expiration
Edit the self-registration. Click on Register Page - Form. Edit the "Expire after" field. Value can be 1 or higher.
Timeouts
This you handle on the Controller under Authentication/Advanced. User Idle Timeout.
To get more detailed statistics on your Clearpass you should enable "RADIUS Interim Accounting" in the aaa-profile.
Auto-send username/pw
In a self-registration scenario I don't really see a need for the Operator to do anything, since the guest can just re-register and the account will be updated both with new expiration and password.
Still - I don't think it's possible to auto-send on other actions than create, so you will have to click on Send receipt after the password update
To accomplish this you will have to add is under Customization/Guest Manager. Check the "Password Display" option, and note the comments on this field as in what kind of access the operator will need.
Once the Operator has done Reset Password / Update Account he/she will be presented the options to print or send by SMS (if this is configures).
You can configure different Email templates to customise your need.
User handling account expiration
As mentioned above - with Guest Self-Registration they can just register again once expiration occurs.