You have told us "100 users". But you haven't told us anything else about the requirements. What is the bandwidth you need to serve? How much extra latency can you introduce? What is the workload? Occasional web browsing, a little bit of e-mail, or intense traffic, perhaps using cloud computing off-site? Do you need to pass any interesting protocols (NFS, FTP, ...)? Does it have to have VPN capability? Or perhaps NAT? What are the security needs? How many internal networks do you need to route for (many sites have multiple networks)? Does it need to serve wireless also (also function as an AP)? Is user authentication required? How about availability and reliability requirements? Do you need guaranteed 5 (or 3 or 7) nines of uptime? What is the financial penalty of an outage? What other services do you want to serve? You might want to use the same hardware also as a DNS, DHCP, NFS, Squid cache, E-mail, NFS, ... server.
Why? Please explain. If a better solution could be found using a different OS, why would it have to be FreeBSD?
