<p>For example, if I have an echo statement, there's no guarantee that the browser might display it right away, might display a few dozen echo statements at once, and might wait until the entire page is done before displaying anything.</p>

<p>Is there a way to have each echo appear in a browser as it is executed?</p>

Start your investigation here:
http://httpd.apache.org/docs/1.3/misc/FAQ-F.html#nph-scripts