It's not too difficult to understand that you can't have infinite energy unless you have 100% efficiency, which in itself is impossible to achieve. And even if you did you wouldn't be able to use any of that energy.
Completely right.
You would need over 100% efficiency to actually have any use for it, but that's impossible.
I think it's possible to have very nearly 100% efficiency using magnets and a vaccuum, but that's just useless.