I think 400 is fine. It makes it interesting later on because people go pop with all the competition. I started an airline at Munich in ATB in February, 40% the way through the game and still got in the top 50. If you keep searching they'll be somewhere soon. Atlanta, for example, had 9 or 10 players based there at the start and now there are only 6. People get bored too and huge gaps appear.