That just means they expect them to last 10 microseconds before decaying instead of 0.1 microsecond. It's not like they are going to exist long enough to build something out of them.
Perhaps. There is also no logical explanation why exposure to a red sun instantly saps them of their powers. It would seem they would retain their powers with but not be able to recharge. So their powers would graduallyThe effects of K on Kryptonians might have something to do with what makes them special under yellow stars in the first place.
dissipate depending on how much they used them. Should have no more effect on them than being kept in the dark or during a solar eclipse.