Most people buy an entire school of fish at a time, I know I do. Adding them all at once is what is done. The bioload difference from 2 or 3 small fish to 6 small fish is not significant enough to warrant a staggered stocking. Not only have I done this a few times, I do it all the time. I do it literally on a weekly basis.
It's unfortunate that a minicycle happened to you when you stocked a few small fish in your tank, but it just isn't the norm.
It might cause more of an issue in a fairly new cycled tank, fishless or fish-in regardless, but it's still not something to overcompensate for.