Nah you don’t need 2000 calories a day. You need that to be healthy. We’re talking about survival here.

You might be less sedentary too, though. That can double or triple if you're trekking through arctic conditions. I don't know, that's what I plan with.

Either way I think I’ll do ok if we survive the initial shit. Can’t say the same for everyone but with some effort I can also help local people get the same thing up and running.

It's not impossible, especially if you're somewhere warm or in the other hemisphere. The people that survive the initial exchange will disproportionately be actual farmers, since they almost all are rural, and there's less mouths to feed.

Where I live in Canada is kind of fucked. I either need to hoard a lot of grain afterwards or evacuate to somewhere else.

There’ll be no government left so we’ll be on our own.

I'm going to contradict you there too, I'm afraid. They'll crawl back out or their bunkers and try calling the shots. Whether people listen is another question.

Potatoes have a bit less than 800 calories per kg, which then works out to about 900kg/year on a 2000 calorie diet. If you can get the yields you were talking about you'll be fine on less than an acre, but they sound high to me. Growing some other stuff at the same time might be worth it for your sanity in a hard new world; staples don't very all that much in productivity.