How would I add a <<Prev / Next>> buttons to cycle the messages without a page reload?
1) Use JavaScript and AJAX. Upon clicking a button, send a call for an AJAX request to a PHP file that gets a new random message, send the message back to the call, and update the innerHTML of the message container.
2) Using just JavaScript, rawoutput a JS array of all the messages, and store the array key of the current message in a JS variable. Then upon clicking a button, get the previous/next element in the JS array, and update the innerHTML of the message container. (Pro: This means there won't be any wait for the AJAX to call, it'll be instantaneous. Con: It means that anyone who views the page source can see all of your tutor messages.)
So #1 is more complicated, #2 has a pro and con to it.