Hi, thanks for using the extension and leaving a review!
For the "use folder as a folder, instead of a small window" functionality, please open the settings. Then toggle the Open Folders as Page. That should be what you're looking for.

I am looking into adding some functionality for choosing a custom icon as cover for folders.
The bug you mentioned has been fixed already, will be included in the next release. Slideshows, video backgrounds, animated icons are not planned at this time.