Let me share my own experience. I have no router, but I do have a firewall (how can you not in this day and age). It does not block outgoing connections, but it does block incoming connections. The only incoming ports I have open for this game are:
UDP and TCP 3658
UDP and TCP 3659
UDP and TCP 27900
UDP and TCP 6500
I am also allowing IP 188.8.131.52 which is from GameSpy and based on the domain name, appears to be for stats .
That confirms what vwjoker states above. I can't say for certain that every one of those ports is necessary, but I can say for certain that (last I checked) our server was visible and able to be connected to from the in-game browser, GameSpy, the All-Seeing Eye, and XFire. As far as latency goes, there are spikes when new players join the server and when the map changes. Those are SWBF server-related performance issues that Pandemic needs to work out. Hope that helps.
[OSF] May the Force Be With You!