If you have 30pcs running, stay away from software entirely. Its going to be cheaper, simply because you won't have to buy licenses for every machine, you won't have to worry about problems communicating between your servers and the rest of the network, AND thats one less thing you have to worry about as far as the users "PLAYING" with the settings.
Hardware firewall is what you want to go with. Specs for different devices, I have no clue about.
GOD I love the smell of NOS in the morning.