Use for the backend something that gives you most functionality as a plugin. Ruby on rails or django. Don't reinvent the wheel. Add js on the frontend as needed.
In the beginning I actually thought about Django or Flask (my background is mainly in Python), which I wrongly dismissed because I thought the main part would have been JS - so I chose ReactJS given the wide availability of tutorial and support.
Flask would have solved some issues such as login etc.
As they say, hindsight is 20/20 :)