Later you can tighten your ruleset using the Mac address of your nic card. Firewalls will only block and log exactly what you decide is important. Be careful how much traffic you log as a hacker can flood your system if you log every instance of activity to the log. Consider blocking only persistent attempts to access your system. Receiving and destination ports .
Planning is a normal process in learning the complexities of rulesets.
When you are reading newsgroup messages, the messages are received on a non designated port on your system. In effect you are listening on post 119 but the port should not be open. You specify the destination ports to receive the newsgroup messages but the system will use any port that is not designated for an intended use to receive the newsgroup. It is important then to understand the Destination Ports are the ports assigned by the protocols for common services. The Receiving Ports are not set by the protocols but are determined by you or by your system.