So back to the OP's question: How much ammo do you need?
For me it is just enough for home/personal protection, keeping qualified to safely maintain a CCW, and have a small spread at the range. In other words a few 50 round boxes at any given time.
IMHO keeping thousands of rounds for a "just in case" or "the price might go up" or there might be a shortage" or any other reason makes no sense at all.
Many people think this way.
Many of these people either cannot find any ammo to buy right now to continue their modest need to keep "qualified to safely maintain a CCW". Therefore, they do not have any ammo to go to the range and then are not "qualified to safely maintain a CCW". OR They pay through the nose to get some ammo. Most likely, the shooting sports is not a priority, so they just go without.
A friend of mine has 6 boxes of 50 9mm. He goes to the range and shoots 2 boxes. He cannot replace those 2 boxes. Now he does not want to go to the range because he cannot replace what he uses. Me, I go to the range whenever I want. I bought a bunch on Black Friday. It was an incredible deal. I put it in an ammo box. It is good to go whenever I want to use it, share it, or help a friend that needs some. If my kids want to spend time with Dad at the range, I'm there. No reason to miss out on fun family time due to lack of planning.
I only have a couple of boxes of self defense ammo. For this type, I am in agreement with you. I don't need much of that. It cost a lot more than basic target stuff. Most of my stuff is basic round nose ammo for enjoyment at the range.
In a way, these casual shooter people that think 4000 rounds is excessive should be thanking the people that do stock up when prices are low. If nobody bought extra ammo when it is plentiful, the manufacturers would have too much capacity. They would then need to lay off workers and shut down manufacturing lines. Then, when lean times hit (like now), the shortage would be even more extreme.
The shooters that prepare ahead of time, that have the "4000 rounds" are not the ones buying anything right now. It's the scalpers, new gun owners and those that do not plan ahead that are buying right now and paying the inflated prices. I am NOT buying any ammo right now. Too darn expensive.
Maybe it's just me, but: I fill my car when the gas tank gets down to half full. I have more than two days of food in the pantry. I have an extra bag of food for the cat. I have a couple of gas cans for the generator. I have extra batteries for the flashlights. I keep extra furnace filters on hand. I have more than one pair of shoes, more than one jacket, more than one umbrella. Hell, I even have two sets of keys for my car even though I can only use one.