1) The EA open thread seems pretty inactive and I'm not sure why that is. On LessWrong that's where most of the discussion happens. It would be the obvious place to post those sorts of things if it were more highly trafficked. I'd still submit articles here and ask questions in the comments section.
2) A simple heuristic might be put straightforward questions into here or alternatively the Facebook/Reddit as they seem more highly trafficked. If you have an idea you think others might share or want to discuss put it into an article.
3) I don't know the answer to this. I've always been able to find what I was looking for, but I do see how it is more difficult.
4) Other places for EA Discussion are the Facebook Group, EA Subreddit and the Complice Room (never visited this one). If you discover any others, let me know, as I find myself confused as to why this site isn't more active and wondering if there are other spaces out there I'm not seeing. It's also worth considering going to a EA meetup as you'll get a lot more quick back and forth that way.
If you want to go beyond the basics into discussion of specific problems (Animal Welfare, AI Control, Entrepreneurship, Rationality etc.) there groups around with more focused discussion. This is a non-comprehensive list along with all the blogs out there. This site is a catch all and also has meta discussions (cause prioritisation, outreach etc.).
Welcome and Good luck in your search.
I posted this comment on the LW thread as well, I feel pretty uneasy about seeing this course promoted. There is value in the techniques taught and there are also serious concerns about the methodology, marketing, and psychological safety of the course. It's messy to talk about because it's simultaneously problematic and can be helpful so participants tend to come out on a particular side. I'd encourage anyone considering purchasing/supporting the course to read this review from an ex-participant or DIY the course with the techniques here.
TLDR of the review