How many players will the OoL server be able to handle though? If it can only take say 100 players at once(I'm fairly sure this isn't the case), and there are more than 100 players wanting to play, it would be wise to have another server. But if the single server will be able to handle the maximum amount of players that will ever play at one time, then single it is. But I would suggest, if possible, to make it possible to add a second (or more) server in the future.