4219
What is also important to keep in mind are turnaround times, but generally the larger the seating capability, the longer the turnaround time.
Also, I have a way of handling the route frequencies which is as follows: all flights up to 2,000 NM range at 1 X route frequency. Any flights with a range beyond 2,000 NM I fly at 0.5 frequency. I find its the way to capitalize the most!
Flying more than 1 X route frequency adds only a marginal amount of financial gains, and will cost you therefore because you will have to own more aircraft to fly a given number of destinations.
Finally, you will soon make more money than you know what to do with if you operate out of major hubs such as O'Hare or Atlanta. And so in the end, I like to fly the aircraft I want to, even though they might not be quite as profitable as others... Also, once you have loads of cash, you are free to operate some routes that are not as profitable, for instance I usually like to fly from Paris to Martinique and Guadeloupe because in the real world that is a very popular route (Air France / Air Caraïbes / Corsair and occasional charters fly this up to several times a day).
The really tough thing when you have a huge airline, is regularly renewing your aircraft fleet. It is time consuming, but it's somehow also something I enjoy doing. Keeping your average fleet age relatively low is important for the larger airlines, or else one day the maintenance costs will sky rocket.
All the best!
PS: these are just my takings, I'm sure other players have different ways of going about it.
PPS: in the real world the flights from Paris to Martinique/Guadeloupe usually all depart from Orly, not Charles-de-Gaulle.