Some "is it possible" questions wrt to JS and the API

Is it possible to use JS to fetch records and display them randomly or weight their display based on some other variable (field, membership, ect..)

Is it possible to use JS to create a Buy This button and add it to a Record?

If someone were so inclined and skilled/knowledgeable (not me) could they use JS/Rest API to run the site Headless/PWA (not entirely clear on the difference there)?

I'm not looking for the code, just trying to figure out what is actually possible with JS and the API.

I have experience with JS but not using APIs in a framework/app like this.

Are there any resources to get started? Hello World type of examples? Under Help>Developer Resources it looks like PHP which I assume you can't use on Cloud 5.

Thanks
JM