Does it really matter which theatre is first, if the scenarios are to be correct, then any allied fields within the area of operations can only allow that type of aircraft. Likewise with the axis crowd. This can be further controlled by applying dates to when those aircaft flew. Eg british fields only allow the aircraft used from britain at the time of the conflict, while any attacknig planes are relavent to those which flew from europe. All said and done a Mediteranean / African theatre would be a good starter.