Hi @coolicious,
I hope you are well today and thank you for your questions.
1. What should I do when I want to display the slider on all sites not only the startpage?
You can achieve this by using the child theme shared in the following topic.
2. What should I do when I want to display the featured image of the pages instead of the posts?
To achieve this please see the answer posted in the following topic for the similar question.
https://colorlibsupport.com/t/slider-for-pages-dazzling-theme/
Best Regards,
Movin