No need to root. Just install the Google Play store using various methods like this: https://www.howtogeek.com/232726/how-to-install-the-google-play-store-on-your-amazon-fire-tablet/
Then grab Fully Kiosk Browser. It removes all bars. Check out this link for a guide on using Motion Detector and Tasker to wake/sleep the display. FAQ: Affordable Hardware Dashboard