Upgrade from 12.1.4103 to 12.1.6

We are about to upgrade my SEPM 12.1.4013 to lates 12.1.6 , we have few questions regard to this, we only have 1 spem server with 20 over GUP on our remote sites

1.  if we upgrade the spem server to 12.1.6, is our existing 12.1.4 clients will still able to work ?

2. is GUP on our remote offices will still work ?

3. anyway to upgrade our GUP ( mainly on windows 2003 server ) in mass ?

Thanks...