How would I go about adding an RSS feed to custom single page app?

Need a bit more information. What language are you using for the page? JavaScript, PHP etc...

No different to what you've kind of done with StarterStory but with different content source.

It is for I want to turn that feed on the homepage into an RSS feed.

Is the data held in a database?

Yes, sort of :) But the data is programmatically generated with javascript

You'll need to create a route in your application that uses your JavaScript data to create an XML doc in the RSS format. What sort of backend are you using?

My app is just create-react-app, so no real backend...

Pat, this is a tough question. However, it's not rocket science for sure. Ping me on telegram, I can brainstorm with you on a call.