Size of Header / Start-Picture

Hi Anna,
I am also new to Ghost but I think I can help you with the “Sections” question. The theme “Ease” has under the Featured Articles “Sections” based on tags. In other words, it will automatically create Sections listing the articles associated with a tag.
I’m sure Ease is not the only theme that does this but that would be the function you would need, listings by tag.
The discussion here might also be of help Recommendations for content-dense themes?

(added: Cathy posted a more thorough answer while I was writing…)