FastAPI

While I personally tend to favor FastAPI for my projects, I think Django is the right choice for many. You'll get more feature out of the box, including an ORM, which should allow you to develop your project faster. FastAPI is indeed fast, but utilizes async Python that may be unfamiliar to some devs. Django also has added some async features recently, and those are optional. Also, while FastAPI is great for APIs because it can auto-generate your API docs for you, it sounds like you are not going to have a public API so this may not be needed in your project. And Django has plugins like Django Rest Framework to help create nice REST API endpoints.

I want to point that, you can still have a fullstack app with next.js with T3 Stack (Next.js + tRPC + TypeScript + Prisma) so your api/server is collocated with your front-end. You can prototype quickly and pivot after to all first if your app grow

I'm a little biased because I work at Postman, but I've also used RapidAPI in the past. It won't matter which OpenAPI editor you use, or even if you develop the OpenAPI spec on a third-party platform besides the ones you've mentioned. But I find the automation in Postman far easier to use, and being able to publish your API afterward to everyone makes it a lot easier to let devs find your API and use it right within Postman immediately. The auto-generated docs, the auto-generated client-side samples, and for a handful of languages we even auto-generate some server-side code too.

FastAPI is a solid choice. You'd have to combine it with an ORM like Alembic for database access. Like any tech stack, there come tradeoffs. FastAPI is a smaller framework than something like Django and is optimized.

However, if you want even better performance I'd say you should checkout Rust Rocket. This is a web framework written in rust, which is very fast and can handle much more requests per second than FastAPI. The trade-off here is that you'd have to learn rust if you don't already know it. Also, if you need to develop an admin UI for this application, you can use Django.

Having performant rust will save you money in server costs

i recommend you to use laravel with swoole and postgresql. laravel orm is so feature-rich and easy to use and it has good speed with swoole and postgresql.

Django comes with Auth/Authz built-in, a free admin interface, and probably dozens of ready-made modules for edge cases (i.e: per-object permissions). It is stable and mature. All it requires is that you buy into its ORM. If that's acceptable to you, then Django is probably your fastest bet.

I had the same dilemma and I chose FastAPI over Django because of its better performance. However if you prefer ready to use components over high API efficiency Django is more mature regarding this.

From what you describe I think you want to go with a full stack framework that has everything you need in one go which django will give you out of the box. Don't get me wrong, FastAPI is awesome but you have to sort of plumb several things together to build an API. Even though there are boilerplates and cookiecutter templates you have to understand all of its components sooner rather than later. I would use it only for building API components of a system.

As all said, both are strong, yet they are different, Django is batteries included framework, which handles from the request till the response is generated and returned to the user as a rendered HTML, on the other hand, FastAPI is a framework for API developement which needs another framework like `React or Angular to parse the response and renders the HTML. For a beginner, Django will be simpler and powerful.

I have worked with both frameworks, for your use case I would recommend using FastAPI. DRF, is no doubt an amazing framework and makes various things easy, but Django's MongoDB support is not that good currently, and since its a big framework, there are various things DRF and Django automatically do when you are using their predefined backend engines, which is not in the case of the MonoDB a NoSQL db. FastAPI will give you the flexibility and speed, for the community front, its also growing quite well there.

FastAPI might not have a big community but the documentation is awesome and covers every aspect of the framework itself. I'd recommend coming up with a pilot project yourself and try it on your own. It has a bit learning curve as FastAPI itself is a combo of a few existing projects otherwise it is amazing.