There is no fixed update cycle, when a new version is ready, it is released.
Yes.
Not directly. It’s easy to add, but it will be available in the next Hestia release, which should happen next week (I hope so ).
No, there isn’t such a feature. You can add nginx.conf_* and nginx.ssl.conf_* files in /home/user/conf/web/domain/ to include extra configuration without modifying the template, but this is not possible for normal users or via the Web UI.