What is the lifespan of a magazine?
That would have some bearing on what you would need. I have 5 for my 9mm Cougar, 5-30 rd mags and 1-10 rd mag for my AR-15 and 4-25 rd magazines for my S&W 15-22. In my mind that would probably be enough for a long long time, decades probably unless they wear out. If they are only good for 1 or 2 thousand rounds apiece then I would need more.
Does anyone know how long magazines last before the "wear out"?