can you turn the LEDs off?

No you cannot, sadly they are always on.

Is this power supply meant to be mounted in the bottom of a case only or can it be mounted in the top?

I have this power supply mounted in the bottom of my case, but it did require an 8-pin extension cable to avoid putting pressure on the motherboard connectors. If they had made the cables about two inches longer it would have solved the problem, but the solution was cheap and it has been rock solid since.