Hello I am really new at this and I would like to know if there is a way to add a license into the AppImage and also if I can have some scripts instead of an executable.
You can use any license you wish for the software contained inside the AppImage. The same as you would do with a zip file or ISO file. Your software could show that license from he help menu and/or first run.
Yes, you are free to use a script or symlink in place of the AppRun binary, as long as it can run your app.