> If there hypothetically was a magical source of near infinite renewable energy that could be harnessed without negative side effects, would you be ok with 2600+ sqft homes and air conditioning?
Yes. In a world with zero negative externalities for massive resource consumption, then by all means, give everyone a mansion and a yacht.
> What number of humans can the Earth ideally sustain in your estimation? If it's substantially less than the current population, then the cure is worse than the disease.
In our current industrialized, consumerist, global economy? Far less than 8 billion. You're painting me as a rabid anti-human eco-fascist though, so let me assure you I'm none of those things. I want humanity to succeed and I want all people to be happy and successful. But the current rate of resource extraction and ecological disturbance that we're directly responsible for will drive our species into a brick wall very soon. Along with millions of other species. We will come to a point where we simply cannot extract the energy we need to feed everyone, and where the biosphere has been so damaged that the necessary agriculture yields just won't be there. And also the other things, like the tropics becoming uninhabitable, ocean acidification killing marine life that the food chain depends on, etc.
I'm not anti-human, I'm very much a humanist, and pro-nature. Humans are part of nature. Unfortunately, we seem incapable of limiting our consumption to sustainable levels when given the opportunity to overshoot. Or at least our current civilization does (past ones have done better, but they also didn't have to try to resist the temptation of internal combustion engines like we do now). I've lost hope for any political solutions given how lackluster all efforts have been thus far, so we don't really need to sit here and debate solutions, because no one's at the wheel and the brick wall is getting very close. Enjoy the surplus of energy while we can still extract it.
TL;DR the famous book "Limits to Growth" was very prescient and it mostly hit the mark.