What to control on the gateway in terms of security with zabbix?

Question

Computer networks

What should be monitored on the gateway from the point of view of information security?
Initial data: OS FreeBSD + pfsense
Currently configured:
1) Outgoing traffic (wan1+wan2+wifi) > 8Mb/s - general outgoing volume monitoring. traffic
2) Outgoing traffic to "wan1", "wan2" > 2Mb/s to {HOST.NAME} - monitor outgoing volume. traffic on external interfaces
3) CPU usage > 70% (in normal mode < 0.1% :) )
4) Notification for 2 wrong passwords (log auth.log)

Answer 1

At a minimum:
Checksum of /etc/passwd