How can I control what’s displayed in Editor’s Pick / Trending Stories (can I control them ? I thought they were categories, but I’ve just updated to this theme and (obviously) those categories don’t exist.
Yes those are category section where you can change the name Editor’s Pick / Trending Stories to any name as well as choose post category to display in each section. Please follow this video tutorial for to change the section name as well as set the post category for each section.
You have to set the Featured Image on the respective Post to show the Image on Front Page Template. You can set the Featured Image from the Page/Post Editor Page of respective Page.