Hi Jason,
FAQ view overwriting is correct if you want to create a new theme.
When you create a theme and want to create for example new default template you create a file with filename "templates/layouts/default.html.erb" and put your html to data field. Frontend should reflect the theme when you activate the theme. You need to install adva_themes engine for theme creation on a backend.
Other way to override adva-cms is to do it on your app folder like you mention.
Hope this helps.
-- Marko