Generate Instagram Stories Style Auto-Captions in AE

You can use Subtitles in Premiere Pro and Audition to add markers with text to an audio track. An expression can create text from Markers. 

At under $100, AE Scripts Monkey Words looks like it would create what you are looking for from a transcript. 

Duplicating the Instagram Stories look precisely from scratch would probably take me three or four days. I could use the work if you have the budget. 

I'm not clear what you are actually saying. Since AE has no automated way of analyzing language, what does "auto-captions" even mean? The text data still needs to be fed in from somewhere and whether you use Zucker & Ebbert's monkey scripts or built your own templates based on XML, CSV or JSON is entirely up to you. For everything else you need to be more specific what you actually want to achieve using what methods. Such broad "Can I do this and that with AE?" questions tend to not go anywhere.

Mylenium