If you're behind some SoHo broadband router, or if you take the time to install a reasonable default firewall configuration for either pf or ipfw, you should be plenty secure.
Next, install portaudit, then have your daily mail going somewhere you can read it (either read root's mail every day, or pipe it to an account you do read in /etc/aliases) and in the security run output you'll get a list of any outdated software on your machine. Then periodically run freebsd-update to keep the base OS updated and you should be good to go in terms of just an IRC client.
