For you more experience reloaders, how do you go about calculating how to stockpile for your needs? Trying to get a better understanding of your logic and numbers.

For example I must be something wrong. I use to shoot about 3,000 round of 9mm/year between me and my wife. So I'd order sleeve (5,000) pistol primers. As I got close to my year consumption, I'd order another sleeve. This way I'd always have about ~2,000 primers in reserve. Obviously, I did it wrong because I got caught short. What should I be doing? Always have 5k small pistol primers in reserve? Or more like a three year reserve supply, so like 15k small pistol primers? Is that what you guys do? Thanks for your help!