On the advice of "put them all in at once": Wouldn't that be kind of a large biological load to put on a tank at once? And how lucky would you have to be to find that many different tangs in just the right size available at the same time?
I agree - always maintained it's 'flawed' advice. Makes sense conceptually, but not so much practically. Fortunately it's unnecessary. Introduction order, and recognition of fish sizes is much more important.