2 or 3 summers ago a friend came over, mostly to drink my beverages and avoid going home. He sat in my garage, as I cast bullets, and looked at the ammo cans along the side wall and front of the garage. And said I had a totally different definition on "How much was enough Ammo!" So I said, "How much do you think is enough?" The answer was a mere 200 rounds per caliber of rifle, and 300 per caliber of handgun. (He has seen the error of his ways and repented! He's working on 2000 per gun or 3000 per common caliber like 223, 9mm, 45ACP!)
I have a similar system. 400 per gun I don't shoot often, and 2000 per gun (5000 per pair of SASS guns) that I do shoot often. It isn't a hard and fast rule, but seems to work out that way! Nobody would object to 5000 38 specials, 45 Colts, 44-40's or 12 gauge. I just think the same way about 223's, 308's and 45-70's. Things like 22 Hornet and other varmint cartridges can float around 2000.
I happen to like shooting 410 and 28 gauge shotgun and usually have 3000+ of each on hand. But shotgun hulls don't last like metallic cartridges so around 1000+ New and 2000 reloads seem to be where I hover. (my brother has shot shell delivered by the pallet! 10,000 seem to be his normal 12-gauge hoard!)
22's are a world unto themselves! 5 ammo cans of stuff for the grandkids to have fun with for starters. Several thousand each for the really fine guns.
Ivan