we will use your experiences and your source (if your license let us) for this project
All NethServer code is GPL licensed. Development is open, discussion is public, decisions are taken openly.
We started discussing the firewall last year, but we didn't progress a lot: https://groups.google.com/d/msg/nethserver/uaeSXPTwa14/B0xazB9IkH0J
Some documentation on what we have now is here: http://dev.nethserver.org/projects/nethserver/wiki/Gateway_Design
If you want to test something, adding the gui to CentOS is explained here: http://docs.nethserver.org/installation.html#install-on-centos