Definitely get e39 530i if you do regularly have 4-5 people in the car and all their baggage.
Mechanically far as I know, e39 have it easier in the engine compartment due to larger space.
Easier ccv job, no need remove so much junk.
Same vanos seals problem
Everything is same
No subframe cracks like early e46
Suspension should be about same cost and maintaince as e46.
Basically same car. More space. Bit more weight. Same mileage.
Go for it. Enjoy the price difference u get after selling ZHP.