> If you want long-term, sustainable agriculture, we need to heavily move to organic farming

This is deeply unsupported by the evidence I’ve seen. Organic farming tends to look far more resource intensive than modern methods. Often for little discernible gain in flavor and nutrition.

> You can get the number by just halving our population

I agree with your conclusion given the data, particularly around mineral exhaustion. (Though there is also the issue of severe mismatches. Lots of lithium, for example, yet no battery industry to speak of.)