Ideally? 1500 bullets per high-use self-defense weapon, one for each capable member of the family, and it goes on. Ideally, one day you'll work 5,000 to 10,000 shells per high-use weapon. It takes time and money to make that happen, so be patient. Buy an additional ammo box or box when you can.
Using my own preparations as a base, your average solo coach should have around 3,000 rounds for his rifle on hand in reserve at any given time. For your pistol (secondary weapon) another 2,000 to 3,000 bullets will suffice. You've probably seen the breaking news where a guy was arrested and the arresting officers found what is described as a “stockpile of weapons and ammunition in his house. Again, whenever possible, replacing stolen ammunition from your stockpile is a difficult matter in today's madness.
It would be a terrible thing to run out of ammunition when you need it, but it's much worse to die of thirst or avoidable injury because you wasted too much money and time accumulating it. If you spend all your money and storage space on ammunition, you will seriously neglect and neglect other problems that are statistically much more likely to kill you under any circumstances. As we've seen, ammunition can quickly go from abundant to scary over the course of a few months or less. Yes, there are belt feed options, but if you have the money for that, I doubt you're reading an article on ammo minimums.
If you're going to be alone, there are more important things to focus on before you go for that big stash of ammunition. Years ago I decided on 12 magazines and 1000 rounds of ammunition per weapon, they did not include hunting guns or shooting toys. On the rifle side, you'll see high-end hunting ammunition at 308 Winchester, 6.5 Creedmore, 338 Lapua, and others representing the New York strip and rib. For example, if your primary weapon is a 9mm GLOCK 19, you would have 250 rounds of Speer Gold Dot 124gr+P ammunition on hand at all times, and the rest would be a supplemental charge like Speer's Lawman 9mm.
You would need to break down the gun and what do you plan to use it for to decide how much ammo you need for it. In short, if you invest your money in two stockpiles of ammunition of 1000 shells per caliber, one battery to store it in the warehouse and the other to practice at the shooting range, you will be much more skilled (and lethal) with your gun and you won't have to worry about it running out in the event of a shortage or network crash situation. Even if you use ten-round magazines instead of thirty-round magazines, you check a ton of ammunition with a rifle. If you have multiple guns, you should ask yourself which gun or guns really need a ready supply of ammunition.
When I was younger and had less disposable income, I always picked up at least one box of ammunition when I went to a large store that carried ammunition.
