Hi Jan,
1. I’d like to create a plugin like this – just need some time. For now, you can use something like this: https://wordpress.org/plugins/display-posts-shortcode/
2. There’s so many great slider plugins out there that I decided to work on things that would be specific to GP and make sure users could use their favorite slider plugin no matter what.
That being said, a slider add-on definitely isn’t out of the question for the future 🙂
You can find other theme documentation here: https://generatepress.com/knowledgebase