noob here .. if the database is in charge of serving rest, where does the business logic go? am i right in thinking that this would eliminate the need for a django/express?
The database stores the data, the rest API handles the business logic. Django has multiple plugins for providing a REST API, such as Tastypie. http://tastypieapi.org/ With this, django is the API.
A rest API is good for when you want to share data between multiple clients (eg a website and mobile apps) and want to have more complicated business logic than the database can provide by itself.