Paragraphs Collection (Behavior plugins) vs. Field Group
As you stated, the Paragraphs Collection module should be considered Experimental, and not used in Production environments:


  THIS PROJECT IS EXPERIMENTAL. DO NOT USE IT IN PRODUCTION PROJECTS. THERE IS NO UPGRADE PATH UNTIL A BETA RELEASE.


This is especially true if your plan is to use this on multiple sites, with the life expectancy of 5 years.

The common method in Drupal 7, and currently in Drupal 8 is your first point, to use fields for settings and use preprocesses and/or twig templates to turn those fields into classes/markup you want.

For re-usability, you will either want to use the Features module and a base theme, or create your own module that will handle the config, templates and styling.  I took that route with the Bootstrap Paragraphs module.