Thanks for the suggestion! I did look into Forem. It is also great.
The customization I was looking into 1) rely more on tags for content organization 2) post book/series 3) blog-like user-profile are all built-in by Forem.
But I choose to go with discourse for the maturity, plugins/themes and the awesome community! Hopefully I’ll soon pick up enough ruby/rails/ember to make meaningful contributions.