My minimum on hand is 7000 rounds .22lr, 7000 handgun rounds of various calibers, and 7000 rounds of rifle/shotgun rounds of various caliber. This fills a 4' x 2' x 2' metal tool box full of 22 "Fat 50" ammo cans plus several cases of 7.62 x 39 mm. When the ammo shortage hit the United States two years back, but not here yet, I bought all that I could afford because I knew we would soon be in the same jam in Canada...
7000 rounds of rifle ammo? I think you will die of old age before you even blast that all out, unless its all .223 and you get so bored you start shooting at clouds 'n stuff. After half a box of magnum rifle rounds most guys don't even like shooting anymore. Then again, maybe you have 10-15 different rifles..
I just keep about 200 rifle rounds per gun, and keep reloading them till the cases split, usually happens after about 8-10 reloads.