I am not really sure how to divide my Django projects into applications.
What things should I consider when laying out a Django project?
I can understand why you have such doubt, Django's documentation about the application concept isn't very clear when it comes to how to organize a database / ER model into specific apps.
Let's say you're building an API using Django and DRF and your ER diagram has many FKs and you're not sure how apps really work. In that case, I suggest you to organize the API code into a single app.