The absolute bare minimum anyone should have for an autoloader is two because if you only have one, and the mag goes bad, the gun is now useless.
After that, I think the more the better, but the upper limit depends on the person and the situation. For my defensive or training guns, I want to have at least 4 to 6 per gun. For my C&R "fun guns," such as my P-38, two mags is plenty.
The only drawback about having TOO many mags per gun is that now you have money tied up in mags that you could have spent on something else, like more guns.
After that, I think the more the better, but the upper limit depends on the person and the situation. For my defensive or training guns, I want to have at least 4 to 6 per gun. For my C&R "fun guns," such as my P-38, two mags is plenty.
The only drawback about having TOO many mags per gun is that now you have money tied up in mags that you could have spent on something else, like more guns.