[laurentl]

The answer to this question is almost always: "the stack you're most comfortable with".

In your case, given that you have (apparently) a strong Python background, you should try to see how far you can go with Django and some vanilla js. If your front-end doesn't absolutely have to be a SPA, you'll be up and running and productive much more quickly with a fairly simple (server-side logic and page generation) and user-friendly (Django) stack. No need to jump into node, npm, etc.

If you want or need to get more fancy with the front-end, vue.js is relatively easy to pick-up, fairly future-proof (as another poster pointed out, vue and React are the two main choices), and can be included fractionally in your existing pages without a complete overhaul.