Hey @Stuart King,
I wouldn't go through all settings, never. This is exactly the kind of approach I've seen in the past with GPOs and that lead most of the customers to set thousand of settings. End result was they couldn't manage it and generated a lot of compatibility issues and later on nobody really knew why something was set. The key word here is light management and focus on the settings what is really important like security.
As a first start for security settings I would use the Security Baseline and then re-configure it to the customer needs. Then talk about productivity tools they are going to use and then discuss what is needed with them. Like OneDrive for Business Known Folder Move. Typically you want to talk also about some corporate branding stuff like logon background images for example. New technology, new strategies and new possibilities.