Best Tech Stack for Chat App like Discord? [closed]

I have an idea for a startup, and I was wondering what the best tech stack would be in my case. At the base of it, it will be a chat app like Discord, except where each user can only be in one server and they can have many channels for their groups. Obviously, there will be much more depth to this, but I'm still working on it. Right now, I am using AWS Amplify as my IAAS. I'm using it for Authentication with Cognito, and chat storage with DynamoDB via Datastore. However, I have been researching and I think that it would be better/more cost effective if I set up my own infrastructure, rather than using Amplify. I am very new to backend development though, and I'm not sure what would be best here in my case. I don't know if I should use a SQL or noSQL database, or what I should use as my Authentication service. My question is what should I use in place of Amplify? Should I use a PostgreSQL database or MongoDB, or any other suggestions? Should I use a server or go serverless with Lambda? I'm very confused and I don't wanna screw this up.

Thanks!