Upgrading to Backdrop CMS from Drupal 7

As we near the end of life of Drupal 7, it's time to decide what to do with your Drupal 7 websites. One of the more cost-effective choices is to upgrade that website to Backdrop CMS.
Backdrop CMS is the Drupal fork: It's a version of Drupal 7 that runs faster, yet contains far more features. It is both easier to use, and more affordable to maintain than Drupal 7 was, and has a built-in upgrade path (no migrations required).
I've previously demonstrated how I upgraded a simple Drupal 7 site in a single day, this time I would like to share my experiences upgrading larger and more complex sites to Backdrop.