BuddyPress.org

I am starting a new project to build out a Reddit like community forum for a Korean-American organization.

Since I’ve been working with WordPress developing custom themes and plugins, I figured starting based on WP platform will get me a quick start vs going with Laravel + vue.js route.
(Performance is not an issue at this point because I do run several high performance dedicated servers with small loads.)

However, I wasn’t able to find good documentation on customizing, writing plugins for BuddyPress, and other development related resources on my search. I understand that BuddyPress was not actively managed for quite some time, but the devs started working on this project in the recent years.

So, I would really appreciate if someone can point me to a resource that I can learn about the best practices for customizing BuddyPress that won’t get wiped with the version updates.

I believe there is some kind of “child-theme” approach, but could not locate the recent guide on this.

What I am trying to do is as it follows:
1. Customize the interface and show “Korean” text for all functions and features users can use (not loaded from the default language settings. I need to change many wordings.)
2. Allow access to private post without logging in based on session cookies.
3. Display special message/media after every 10 post lists or replies or comments.

So, please advise me where I can put the codes and filter BuddyPress loading forum lists.

Thank you!