Like all API design, putting a REST API on your app is tricky business that most people learn through lots of mistakes. So stand on the shoulders of other peoples mistakes! Thus, REST worst practices:
In the REST world, the resource is key, and it’s really tempting to simply look at a Django model and make a direct link between resources and models — one model, one resource. This fails, though, as soon as you need to provide any sort of aggregated resource, and it really fails with highly denormalized models. Think about a Superhero model: a single GET /heros/superman/ ought to return all his vital stats along with a list of related Power objects, a list of his related Friend objects, etc. So the data associated with a resource might actually come out of a bunch of models. Think select_related(), except arbitrary.
Mistaking the app’s internal model with what API users want to work with was the mistake I made on the first API I wrote.
Any big API is going to need to have dedicated servers that just serve API applications: the performance characteristics of large-scale APIs are so different from web apps in general that they almost always require separately-tuned servers.
This is how I prefer to roll my APIs lately. At the least, they should be a separate set of controllers. If you can extract a completely different application even better.