Web application architecture patterns

I want to start a project - web application. It will have a forum for people to chat and create threads, a main page with cool animation and stuff - just to show some info (like some info, then you click and go further to show more info), then the page with video lessons, like a library, something like udemy. The tech stack I will be using is React on front and Golang on back. There are a lot of stuff, and I am struggling to choose the right architecture. I want to make it scalable, maintainable, it will be used by a lot of people,so it have to handle it. And I know nothing about the security, please, can you suggest some patterns that I need to consider. Thanks!