I know very little about freewheel changing and replacement. I have a five gear freewheel now and I'm assuming I can only replace it with another 5 gear freewheel. I have a couple of questions

1. Can I only replace a 5 gear freewheel with another 5 gear?

2. Is it possible to destructively remove a freewheel without destroying the thread?

3. Are there any special measurements I have to know before ordering a freewheel off Amazon, or is it as easy as choosing the same gear number?