Customization Questions

Hi,
I just started using this theme with my blog (www.highandlowblog.com), and I’m trying to do two things:

1) I would like to set a static featured image for the homepage. That’s the page that lists my latest posts. I am able to set a featured image for individual posts and those show up when you click into a specific blog post, but I’d like an image to show up permanently on the home page. That’s the same image I use on my About Pages.

2) I’d like to make the header fonts smaller. I figured out how to reduce the paragraph font size to 10pt, but now the post titles feel massive. I assume I need to change this in the CSS feed, but I am unsure of how to do this.

Thanks!
Rachel