You have missed many things about real SEO, and you’ve also included wrong information.
- Google don’t use social signals for ranking — Reason? Just logout to your facebook account and see many pages in Facebook, you will got some error with captcha to fill up, then you will see the next page. Same thing happen to Googlebot, when they crawl social media websites to collect information.
Social media sites are huge, and if they allowed Googlebot to crawl their website then, they will waste much amount of bandwidth.
2. Google does not care how long your article is. It’s purely depend on user intent, don’t you see the results from stackoverflow with just 500 words.
3. Google ignore meta description 80% time when it’s not match with user query. It is not a ranking factor.
4. Alt tag in images only help in image seo. Look out quora, they don’t use alt and good picture name in images, but still their images are ranking, because Google use surrounded text to know about the images. For example, In flickr when someone comment “What a beautiful pic of himalaya” Then Google will know that image is about beautiful pic of himalaya.
I suggest to not to read marketing type of blogs. If you really want to learn SEO in depth then read checkout their patents.