Well, I think this would be the simplest: the temperature at any given latitude will be the average of the last n years. Period. But maybe I'm too naive.
a) Maximizes arable land, b) Minimizes climate-based natural disasters such as hurricanes, and c) Is as near to self-sustaining as possible. That is, the global mean should not lead to significant growing or shrinking of ice caps and glaciers, nor significantly alter carbon uptake by the oceans. While some degree of human control could make up for heterostatic forces, a swing too far in either direction would quickly exceed our ability to compensate.
Exactly. That's why I'm suggesting that the "not worse" solution could be to artificially heat up the earth to the actual temperature for every latitude. Politics aside, a different temperature would probably disturb the current equilibrium and potentially cause some side-effects worse than the suspected mini ice-age.
there are some lands on the periphery of existing arable zones that might become desirable in the short term, but certainly there will be a net loss worldwide...local economies have grown around existing arable zones, you have to transplant all that too
mother nature is still in charge, and needs only shrug slightly with a temperature change of 10 degrees on average in either direction to eliminate humans and our society