OK, so.....
To connect to the server they are using ubisoft program, as the game doesn't have built-in browser like CS, however thats not what flyers are using out there, the program used is called Hypper Lobby and it was made specificaly for the flight sims. Technically it lets the user chose out of most flight sims out there and then gives him/her a list of servers for that sim. Also it keeps track of scores (kills, flight time, etc.)
Now the meaty details:
The limit is 128 players. The dedicated server can be run through HL. (hypper lobby)
Recommended system basically depends on your bandwith. It takes about 20Kbs upstream per player. Therefore, with a 1meg dedicated upstream connection you can host about 50 players. For that amount of players you need maybe 1.5GHz cpu and 512Mb memory.