What I did in IAD and NGO was simply grind until I purchased one A380. Once I purchased the A380, I simply stopped servicing the regular airliner planes, and only logged into the app when my own plane returned. This way, there was never a queue of airline planes landing at my airport, making the plane servicing sequence quicker. Obviously, once I save enough cash to buy another A380, I buy it immediately. This method, although takes time initially, grows your fleet exponentially, and eventually can make you hundreds of thousands, even millions in about one hour of playing a day. Once I maxed out the XL stands, I simply invested the money into buying a fleet of A350s to fill the L stands.
I currently make about one million W for 40 minutes of playing at IAD and 700 thousand in NGO, and since you aren’t buying multiple planes at the same time, the maintenance is staggered, which makes managing cash easier(at least in my opinion).
It might not be a very appealing way of starting a fleet, but the rewards at the end are quite high. Good luck!