There are tools out there like Cacti, or Nagios that can help you monitor your network. Another good one if the network is Cisco-based is their Cisco Network Assistant tool. These won’t necessarily give you tips when to further segment your network (only experience and education can really help you there) but they are good monitoring and management tools for networks.
Be sure to purchased manageable switches so you can look into individual port stats and settings. That is a place to start with understanding your network.