I think a good rule of thumb should be a bare MINIMUM of the following:
500 rounds for bolt guns, 750 rounds for lever guns, and 1,000 rounds for semi-autos.
500 rounds for revolvers and 1,000 rounds for semi auto pistols.
5,000 rounds for 22's.
This is a bare minimum per gun. Then add to the supply. Shoot only anything above this minimum for practice. Reloading expands this when you buy supplies like primers, powder and bullets. Also consider casting. This is good for large fat rounds like 44mag, 45-70 and such which is slower anyway.
For food gathering, learn to snare and trap, also fishing. This would save ammo.
I don't think it matters what caliber. In light of recent shortages, after filling your minimum supply for what you have, then you might consider other calibers. I am thinking along the lines of the 17HMR, 22 Mag or 22 Hornet. Then say a 300 Blackout, 243, 7mm 08 or 260 Rem. 30-06 for sure. Ammo for these are still fairly inexpensive. Also 40 S&W was still on the shelves during the shortages. 38 specials and 357's were also still on the shelves as well as 44 mag. I also saw a fair amount of 45 acp.
Get the basics first, then expand.
Remember you also need to stock up on food and toiletry items.