You'll be able to move boxes to block lines of sight for sneaking, and to throw barrels around. Barrels can contain water/oil/poison, and maybe other things too, and those can be good targets for spells.
No to take boxes out from under people, they don't stand on boxes. You can pull chairs and benches out from underneath people, except that without schedules, no one sits on those things.
Barrels can maybe be thrown at enemies to cause damage, although I'm not sure that's still possible. They can't be dropped on someone's heads, I believe. You can't make things roll downhill, this game doesn't have that kind of physics.