Dragging a foreigner (especially) into the country to be put into a metal cage for violating copyright is disgusting.
Unlikely. He'll probably be sentenced to a minimum/low/medium-security prison facility/farm. Over 80% of American federal inmates are in a facility meeting one of those classifications [1].
The federal sentence (using that for comparison since the federal government carries out IP law in the US) for first-degree murder in the US is either life in prison or death by lethal injection. Dotcom is exceedingly unlikely to spend the rest of his life in prison and is obviously not eligible for the death penalty. He'd probably be looking at a decade or two at most. Obviously, that sucks for him, but your assertion that he'll be treated worse than murderers and be SA'd regularly in a prison housing violent inmates is simply not true.
[1]https://www.bop.gov/about/statistics/statistics_inmate_sec_l...
So, no, what you said isn't absolutely true.
Hmm, excellent question. And for context, America is going to give Kim Dotcom a functional life sentence in what Americans like to call "pound-you-in-the-ass prison". For sharing files. He'll be given more years than harsher than most murderers.