If i setup my freenas system with 2 network cards, one connected to a a network that has internet access and other in a private network, can freenas work as a gateway to this private network?
Yes, it's BSD, but FreeNAS was never built to be a gateway so he would need todo it himself. Chances are a lot of the libraries he may need isn't installed at this stage, and he'll probably run into problems which the community can't help him with.