the good thing with it being virtual is it doesnt cost an arm and a leg to use an airport as a hub.

short answer yes you do pick yoru own hubs.
depending on what sort of fleet your friend will be using will depend on what airports you use. ie: short haul fleets, RJ's CRJ's Md80s A320's 737's and so on, you'll want fewer hubs closer to your main base. remember you dont have to only fly to hubs, they are just where you fly the main bulk of your aircraft through,