Add another button for UI field set in admin
You're looking for the Paragraphs module. 

You can use it to create a paragraph type with the required fields in it (reference, specification, etc), than add a multi-valued field to your node type referencing that paragraph type. 

Because it's a field, you'll get the standard add another and sorting functionality.

The How to start with Paragraphs for Drupal 8 docs page should get you going pretty quickly.