I recommend on using the Internet and looking up airports that are located in major cities but have runways short enough to where larger airlines cannot 747 spam your routes or smaller airports that are located in major cities but have a different name than the city, such as Burbank-Hollywood Airport, which is located in Los Angeles.
Oh yeah, leasing aircraft until around 500M is never a bad idea. Also let the game run every now and then, and let your money build up over time. It is never a bad idea to have a large "cushion" just in case.