I am a Ruby on Rails developer in a outsource company in US market. I have 2 years develop Ruby on Rails with React JS.
1. With your problems, we can use Action Cable in Rails 5 above to handle easily. Every post is liked or commented, we will fire an action through Action Cable that send notification to the user.
2. The data we will save to database, so we can count, process whatever we want.
Hope can work with you.