Please call your local store for pricing and availability.
4x4 cedar is often used as a post in fence construction.
Yes it can, very good use for it in column.
Ask at the help desk to special order
A 4x4 is square and does not have an actual diameter. A rough cut cedar 4x4 is close to 4" on a side. This differs from a finished 4x4 which is 3 1/2" on a side.
You can call or order from store ahead and they can have them at store for you.
If you like i am making some benches for my deck with them
No it is not treated wood
I personally dont suggest it. The have harder wood that you can use. Last lo ger.