i actually am already riding a freehub singlespeed. my questions are for a freewheel conversion.

when i thread on a freewheel singlespeed cog it will just unscrew when i backpedal, correct?

to stop this i must use a english thread bb lockring? is that english bb lockring the same lockring that is holding my current 7sp freewheel onto the hub?

would a bmx freewheel thread onto a freewheel? do i need a lockring with a bmx freewheel?

and when you said redishing, how is that done? is it something i can do at home or pretty easy to learn? tools? how much tools cost?

how much will a bmx freewheel cost? i know singlespeed freewheels are ~<$20. well enough questions for now, thanks to those who've replied!