For OP - Hello, I am a new user of Siril.
For multiple sessions, I use the recommended Sirilic program. I have not needed any scripting - it is all click - click -click to select options (and some drag and drop for files).
For single session if you want to build a script with your own parameters it will do that also, again only click-click to set the options you want and then it just outputs the script.
Reference frame selection i dont know. I cannot see how to do it automatically unless you take some arbitrary quality metric.
For developers - it took some time to find Sirilic and use it, even though it is referred to in tutorials.
A suggestion is to add a menu item called multiple session / scripting which when clicked opens Sirilic directly. That will make it more “visible” and also easier to use.
And also have a separate link for multiple sessions / scripting on the tutorial page. It can just link to the Sirilic page.