There are more than one kind of pipe. To which you want to know, is only a guess. A pipe is a tool used for smoking tobacco. It is a tubular device used for liquid flow.
pipe
If you are screwing in -- yes -- If not -- you do not use pipe dope
Pipe nipple is use as connector to both pipe which have female end. It does not same as pipe reducer which nipple has same diameter throughout both end and threaded. Pipe reducer has different diameter for both end and it is use to join different pipe diameter.
Mainly for making water pipe.
You should use black pipe -- Galv. pipe will flake off inside of pipe
You can use copper pipe.
Absolutely Not!
Minimum 3/4" pipe.
pipe dope and teflon tape
A pipe cutter is the best tool to cut PVC pipe.
Use teflon tape with a little pipe dope. If you don't ever have to take apart again then you can use glue which you are calling cement
PVC pipe is fine