I have a question for the OP, regarding fuel consumption. Take whatever airframe/engine you are familiar with (an A320 would be good), flying a routine flight plan on, say, a 600 nm flight between uncongested airports. Then, what's the total fuel consumption, if that flight is full (say, 200 lbs per passenger in body/carry-on/baggage weight), vs the total fuel consumption flying dead-head? That is, the only variable is passenger load.