Having worked with many J2EE database applications in the past, I now turn to Django if I can and the project allows it as it is so quick to get up and running. It has a logical workflow and organized structure and it comes with a high level of security (if you import the appropriate backends). If you are wanting to incorporate python-based data processing (or cython), it is relatively easy to write a backend plugin. I have found it more stable with updates than other frameworks (particularly compared to the NPM world such as React which so often descends into dependency hell when a version of something is updated). One hassle worth mentioning is the database migrations support which can sometimes mess up during development but there are workarounds. With a React frontend, you would be using the Django REST Framework (https://www.django-rest-framework.org/) so you may find that you have to overwrite a lot of the methods here as the defaults are fairly basic CRUD operations which don't really support nested relationships very well. I don't have any experience with .Net so I can't give a comparison except of course, the obvious one, portability, as Python is platform-independent. PS, I would recommend Vue over React also for a well organized front-end.

You can get done what you want with just about any modern framework and language.

Django is fast and easy to learn but as your website grows you will need more and more community apps whose release cycles do not keep up with Django. Unless you are willing to work on the community apps, Django may not be for you.

Compare the active community sizes of Django apps to Ruby on Rails apps and you'll see very active communities with Ruby on Rails and small Django communities. Don't switch to Ruby on Rails though--it is a small, dying community of enthusiasts.

ASP.NET Core is a great backend framework, the community is large and you can always find answers; however, according to the StackOverflow developer survey, it is not desirable for the majority of programmers. I still use it though because my background evolved from C to C++ and then to C#. I also like the Microsoft world.

I've programmed a lot using Angular and some React but am switching to Vue.js which is much easier to learn and faster to code in. Be sure to use TypeScript with Vue.js. Just watch the video on the Vue home page to see how fast he can code using Vue.

But do you really want to code a website from scratch? If not, try WordPress Elementor. It may save you tons of time.

For mobile, use Google Flutter. In my 35 years of professional programming I've never seen anything more elegant, easy to learn, well documented and beautiful than Flutter. From one a single base you can target both Android and IOS and soon Web. You can also develop in Android Studio which means your screen real estate requirements are small so you don't need two monitors.