I am looking for security SOPs for a large scale wireless network. I
am particulary interested in which TCP/IP ports to block at the
Internet Connections.

I am aware of port 25, but what else should I be concerned with? An
exhaustive (most secure) list would be wonderful.

Unless I'm misunderstanding you, your plan is allow all ports and
block only potential problem ones. Since many services can be run on
alternate ports, a more common (and secure) approach would be to block
all ports and allow access only to the ports you need.

The "official" list of which services are associated with which ports
is here: http://www.iana.org/assignments/port-numbers