AppHarbor vs Horizon vs Socket.IO

We are starting to work on a web-based platform aiming to connect artists (clients) and professional freelancers (service providers). In-app, timeline-based, real-time communication between users (& storing it), file transfers, and push notifications are essential core features. We are considering using Node.js, ExpressJS, React, MongoDB stack with Socket.IO & Apollo, or maybe using Real-Time Database and functionalities of Firebase.

I want to add uWebSockets.js in my application for real-time chatting, for that, I have to draw a UML and ufd diagram flow then I have to implement it in my code, my stack is node js, android, express, MongoDB, Redis. how can I do this? I want to add uWebSockets.js in my application for real-time chatting, for that, I have to draw a UML and ufd diagram flow then I have to implement it in my code, my stack is node js, android, express, MongoDB, Redis. how can I do this?I want to add uWebSockets.js in my application for real-time chatting, for that, I have to draw a UML and ufd diagram flow then I have to implement it in my code, my stack is node js, android, express, MongoDB, Redis. how can I do this?i want to add uWebSockets.js in my application for real time chatting, for that i have to draw a uml and ufd diagram flow then i have to implement it in my code , my stack is node js , android , express , mongoDb, redis . how can i do a this?