If my app is live in Google Play & App Store, and I add new articles, will the latest updates be automatically available to users, or do I need to update the app manually for those changes to be seen?
You don't need to do anything like update or republish your app as it's a transactional thing. Adding new articles, bookings, or any content is an ongoing business need of any business owner, and doing so doesn't change any of the core design of your app.