How to configure a local start up page in case network goes down?

This is possible in the configuration by navigating to Basic > Start Page & Browser > Advanced > Offline Start Page.  You have the option of defining an offline start page which will be used when the default start page cannot be displayed (e.g. due to connection problems).

 

https://www.provisio.com/helpconsole/SiteKiosk%20Help/en-US/settings.htm