1. I don't really use social media. My blog posts auto-post to Twitter and LinkedIn, and that's the extent of my social media engagement. I don't follow anyone on Twitter, for example. Sometimes people will email me if they feel strongly about a post. But for the most part, I solve for being "caught in a bubble" using a small Slack community I'm a part of, where some friends and former coworkers pick apart my blog posts and point out how stupid they are :)
2. I'm not really sure. I don't pay much attention to SEO since the traffic doesn't matter much to me. Don't get me wrong, I get a thrill when something I write makes the rounds and people seem to like it, but not enough to worry about optimizing for it.
3. I just use the built in Wordpress email subscription feature, which doesn't provide any open rates. I only have ~150 email subscribers anyway, and my blog itself only gets 100-150 views a day. In general, I've done basically no marketing for it outside of that I used to post a lot of them to HN until the domain got shadow banned.