I'm currently working on a really Chat heavy application (with some other elements). Our stack is basically:

Backend: Phoenix (For sockets/channels and ultimate scalability) Postgres (For user/profile based stuff) Redis (In-memory datastore for queueing messages when recipients are offline)

Front End: React / React Native, Redux

Frontend : AngularJS Backend: Play framework (Java/Scala) + MySQL + Nginx (load balancer) + Redis (cache), deploy all these pieces with docker (highly recommended)

• if your data model not complicated, you can also just use Redis.
• try use websocket for push tech. FYI, This is a general bootstrapping stack for basically everything, to have different pivoting on the stack, you need expose more business knowledge about your website.

I would say that mean.js framework has everything in place to build this kind of applications. AngularJs for the frontend, node js for the backend with mongo db, and of course that node supports web sockets for real time notifications.

So I think that it's a good stack to at least create a rapid prototype of the app.