The streams “endpoint” is https://api.twitch.tv/helix/stream an endpoint is an API URL
No you should use both. As per what I linked you need to send the App Access Token, and the Client ID that that app access token was generated with.
Cron job is a job that automatically runs on a server periodically to do whatever.
So you’d create as scheduled job to update streams status into your database and the database would serve the front end.