What should I do when updating 150+ posts on my site?

I was completely new to this a few years ago so I did most everything wrong at the start but have been slowly picking things up much thanks to everyone here at WF for the advice and tips (much appreciated!).

Here's my situation. The other day I had a ranking performed on my site and it showed only 58 indexed pages which surprised me because I have over 250 posts since 2012. But then it got me thinking since I only started using the SEO Yoast plugin for the past six months, maybe I should go back to my old posts and input a focus keyword, meta description, etc and update all those pages. I still have 150+ posts/articles that are still showing the red SEO circle beside them since each does not have a meta description or focus keyword.

Therefore, this past week I have been going back and re-editing each post (oldest first) for keyword, <h1,2,3> tags, image alt tags, title, etc. Once updated I take that link and send to the 5 social media avenues I actively use: Twitter, Facebook, Google, Pinterest, and WeHeartIt.

My question is, since I'm taking the time editing each post (about 45 mins each), is there anything else I should do while I'm tinkering with each of these posts? Or anything else I might be overlooking? I would hate to have to go back and reopen them all just to insert or edit something else. I already have a newsletter signup area below each post, a picture/bio, and links to other related posts.

Also, I was thinking about increasing my social media connections and start using others and I've read here about some services that automate this for you. My thinking was instead of just 5 SM links per post (what I now get) why not use a service like onlywire or social monkee and get 50+ links per post. Any thoughts, comments, suggestions?