This depends on whether you use all the standard gear that comes with a plane or replace it with better quality gear when you build. I have 3 different sets and sometimes that is not enough. Problem is that we have 3 different standards, Imperial, Metric and then occassionally some othe weird stuff that nothing seems to fit.

Don't think there is a correct answer to this question but rest assured you will think you have everything covered and then something else will jump out at you and need a different sized driver or hex key. It is just the nature of the hobby