Supplying airports: yes you could contribute to the economy and interaction with fellow aviators by hiring pilots to move supplies for you, but depending on the the amount you need, and especially if you require expediency, there may be an aircraft near/at the supplying airport and renting it will be cheaper and faster than hiring someone.
Group bookings: In general you will only want your FBO to spawn green jobs in groups of 1. Avoiding the booking fee sounds nice, but groups of 2 is only worth it above 32 passengers, and groups of 3 is only worth it above 55 passengers. So unless you fly so frequently that you need passengers to be spawned as quickly as possible, or unless you fly the highest capacity planes, its most profitable to limit spawns to groups of 1.
You need an aircraft to fly between FBOs, Lease or buy? Often the best option is to fly a system owned aircraft nearby and use it on your route. This way you won’t have to pay a monthly fee, and given FSeconomy’s disporportionately low activity level (compared to the amount of aircraft/airports), nobody is going to miss the aircraft, and its unlikely someone will “steal” it from you in which case just use the search function to find another one.
Supplying or building FBOs? Business jets with their monstrous weight capacity are often the best option. Thank the BoD that cargo volume isn’t factored in! Another good option is helicopters, a chinook can move 10000kgs into an airport with the shortest runway.
In terms of pure profit, shorter distance is always better. A CRJ700 actually doesn’t cost that much if you only fly it for 5 minutes.