Hi @wsterdan
Please find an answer to your questions below
1. I notice two themes are included, with and without a child — what’s the difference for setting up a site similar to your demo and why would I use one over the other?
A: You can use the main theme. Child theme is included for those who want to make changes in layout/design of theme by modifying codes.
2. Please point me to where I can find the widget used in the demo for your main page carousel images (and where to find an example of how you implemented it in your demo).
A: You can go to Appearance >> Customize >> Theme Options >> Slider Options and enable slider. You can use options available there.
Please check this documentation if you need any other help https://promenadethemes.com/documentation/blog-way/
Thank you.