Hey Tares,
FreeNAS is designed for storage and storage only. As such, you should not use it for anything else than storage. Firewalling, Load Balancing and other services should be provided by other solutions.
First, these other solutions will give you a better service than FreeNAS because they are meant for that. Here, I am using pfSense and HAProxy for firewalling and load balancing.
Second, FreeNAS' security is somewhat weak because it assumes it will be protected by infrastructure. That is why you do not have non-root user that you can use to connect the WebUI and work with it. Should you expose it, you will not be that well protected.
For your Internet access, firewalling and load balancing, I recommend you take a look at pfSense. That one will be more than happy to face Internet and keep the bad guys outside.