Server Requirements - Always On in a single server? - Needs clustering even one server on another Data Center?

Hello:

I have been asking this questions to different forums and got different responses, so I wanted to know if asking to "Microsoft" will give me some good directions. (All in SQL Server 2012, including the OS)

Question 1.- Always On "HAS" to be configured on a WSFC node? How about in a Single SQL Server. (NO Clustering)?.

Question 2.- What about our mirroring processes configured and running in single servers, do we have to have WSFC installed before we can upgrade them to Always On?.

Question 3.- In a case I have WSFC, and configure Always On, can my second or third replica reside in a single SQL Server? (No WSFC). What if I can not have Clustering in a DR Data Center? or I do have only VM's on the DR Center?

Any help will be greatly appreciated.

Thanks

Oscar Campanini