Create a custom Plugin and output fetched Data similar to Airtable Plugin

I want to create a custom Plugin similar to Airtable Plugin. But it will catch a different API.

How can I make it available as “Data Source” for example in the “Repeating Group”?
Are Actions only available in the Workflow? Or are the same actions available in a repeating groups Data Source? Hard to explain… :-/

Is there a better Tutorial / Videotutorial / Online Course / Training where I can get detailed Information of how plugins like Airtable have been developed?