AC allows simple up voltage/low current for main transmission lines otherwise the copper wire would need to be so thick, the cables would break from the weight.
With DC if the cables were underground, you would need a power repeater station every 100 miles.
Of course if you are off the grid with a dedicated solar array, either would work
No such device. You'd just need power plants a mile apart, just like Edison did in NYC.
You get about 100 watts per square foot at the equator. That is a lot of square feet if you plan to process bauxite.