Make sure your partner(s) or candidates agree on how the plane will be scheduled. One could have weekends free and the other not, which makes scheduling easier. If there’s scheduling conflict, how is it resolved? Do the partners agree to pay an equal share of all expenses or just those incurred when the plane is on the ground? If you take it up do you pay for your own fuel and oil, always leaving it full for the next time? If you both fly weekends only, can you have one of you fly Saturdays and the other on Sundays or alternate weekends?
"Man cannot discover new oceans unless he has the courage to lose sight of the shore."
-- Andre Gide