MIchael,
Can you articulate what kind of devices you are using Airwave for as well as the deployment type? Are you storing multiple versions of device firmware locally? Your data retention policies are an excellent start. 80GB thick provisioning is the default for the VM install - you can at your discretion increase this upto the capacity of the shared hard disk, or even add additional drive space to the physical server and then resize the volumes for AirWave usage.
The pgsql structure is where all the client, device, rogue tables etc are contained so not surprising that it is the largest consumer of your drive space. Airwave provides a horde of client & device granularity which is hugely beneficial when doing triage and troubleshooting. That said - to provide this - it stores all this information locally on the pgsql db structures.
You can also check to validate your reporting settings as well as your nightly backups. Several choose to FTP those (backups) offsite so that operationally, Airwave has more disk space to use.
Note that when you make retention changes, it won't reflect in the deployment until the next nightly backup.
If you're not familiar with how to resize the VM disk or add a new disk to the platform, I can post a recent MoP I wrote for a customer (client specifics removed) to achieve the same result.
Hope that helps, Adam