Being a gunsmith, firearms instructor and former LEO, my thoughts used to be complex on this.
Now, it’s much simpler for various reasons.

First, I have a family now and my priorities changed.
The threats I face also changed when I left LE work.

What I choose has to be used by them also.
They can’t handle much of what I chose over the years, so my collection is changing.
Simpler, smaller grip and firearm size, easier recoil, low maintenance, all play a part in the choice.

Many items were sold off for various reasons, changing to another ‘platform’, increasing the prepping stockpile,
letting collectors pieces go to a collector rather than me beating them up.

A lot also plays into what we do now, the entire family hunts and shoots.
Our hunting guns can provide yeoman service as defensive weapons.
Slower, yes but there’s something to be said for a gun that one has killed many critters with, you’re going to be familiar with it.

There are a lot of good options out there, some better than others, but in all reality how much use do you expect out of your firearms post-SHTF?
That’s the key point. You can have 35 guns, 1 million rounds of ammo and still starve to death because you focused on the wrong thing.
Conversely, you can have years worth of food but no way to keep the neighbors from taking it. Bad idea.

There is a balance that many of us gun owners forget.

Make your choices according to your needs.
Where I am, we hunt. Big game, small game, game that hunts you back.
My/our choices are made accordingly.
We have some fear of refugee’s and such, but depending on the season and what actually happens (SHTF wise), they may not be an issue, not being able to get here.

As such, most of my ‘stocked’ ammo is hunting related. It will work fine for defensive use also.
Too many people don’t understand ammo and it’s availability.
Some expect to find it laying around like on “Call of Duty”, or that they can trade some military or LEO out of ammo. Ain’t gonna happen. Pretty much everything anymore is counted and signed for. You are issued “X” amount of rounds, you better be able to explain where every last one went as it stands. Post-SHTF, they are going to be keeping the ammo for themselves. I would/will.

For serious social work:
We keep a couple of AR’s for the kids. Building 6.8mm uppers for them for hunting.
The wife has her AK, I have my FAL.
For handguns:
I prefer 1911’s but have some Glocks also.
The wife has her 9mm/.38’s
The kids? So far, they’re learning and trying different things.
Although the oldest daughter is a terror with “‘her” .38.

Ammo, I do need more but could hold out quite a while with what I have or can make.
Changing guns/calibers has left me short on some choices. But I’m not worried about that, at least not right now.
Right now, it’s getting ready for filling the freezer, buying tags and making sure the hunting guns are ready.
That and the fishing gear.

Minimal count?
One good rifle per person, one good handgun.
At least one spare of each, just in case.
After that, I don’t give recommendations on brands, calibers or such in general.
There are too many variables and personal opinions and fit issues.

As far as ammo goes, I do have some recommendations:
Rotate your defensive rounds yearly.
Put that old ammo back for a ‘rainy day’ and sight verification.
Put new ammo in and mark the box end with the date. Save that for ‘just in case’.

That means you may go through 100 rounds of defensive pistol ammo a year, storing the older stuff.
Buying a box or two every couple months, you can quickly put quite a bit back. Remember, this is defensive not blasting/target.

Rifle, defensive ammo? You carry 3-4 mags with you daily in your car/truck/etc? Rotate that yearly also.
Say 100 rounds again.

Rifle, hunting? I may go through a 20 round box a year between sighting verification and hunting.
I can pick that up at my leisure (or sit down at the loading bench for an hour and have that).

I can’t see any of us ‘practicing’ post-SHTF, so blasting/target ammo is just extra ammo in case we would run out of the defensive ammo and we won’t count that. But it’s nice to have a lot of it regardless, prices just seem to keep going up long term.

So figuring 20 years, 100 rounds a year, that’s 2000 handgun rounds,
Same for the Rifle.
That seems pretty steep unless you break down the purchases to 50 handgun and 20 rifle a week. If you can buy more, do so. But it will eventually add up. And with each additional year, that ammo that comes out of rotation adds to the ‘stockpile’ at no additional cost.

Edit to follow.