A discourse on how to build and implement each is beyond the scope of this treatise. Each comes with ample build and installation documentation. We will cover only certain tweaks here.
Argus and tcpdump should be configured to listen on the SNIFFER NIC only, in our example em0. The remote management daemon for Argus should be bound to the MGMT NIC only, e.g. fxp0, on port 2002 in our example. It should not be bound to the SNIFFER NIC.
Argus should be run as a daemon, and ideally started at boot. Here is a suggested template for your /etc/argus.conf file.