Some of the webinars are quite old or to do with Learning Pool's own version so not everything you see will be applicable.

There is currently only one menu and theme available in the authoring tool but you can copy them and make your own if you wish : https://github.com/adaptlearning/adapt_framework/wiki/Styling-your-course

Take a look at the plugins list for more but I don't believe any of the extras there are compatible with the AT. https://www.adaptlearning.org/index.php/plugin-browser/

Finally no I don't know of any course which can be downloaded and modified as there is no import function in the tool. 

HTH