I knew of LW's existence before HPMoR, through the same source that referred me to HPMoR (ESR).

1. I registered mostly to comment on this post.
2. I've been reading the Sequences.
3. More stuff about Bayes' Theorem (my extent of knowledge before I read the Intuitive Explanation was the idea that there will be many false positives on searching for rare events).
4. No.