Updated 11-14-15. Here's Lovingpho's own beef pho recipe in infographic form. This beef pho recipe yields about 20 quarts, which is about 20 regular size bowls you can typically get at most pho restaurants. With this size, you can make it once, enjoy it, and have plenty of leftover to freeze for quick pho anytime later.
It's quite easy to scale up or down depending on your desired size. Just do straight linear scaling and you can't go wrong. Of course, you can adjust any element to customize to your own taste. Let me know what you think, and leave a comment below.