"Why not a more or less circular orbit? Is this so the moon-bound ships can dock way out and "hitch a ride" down to low Moon orbit where the lander detaches for the final leg? Is it cheaper in fuel, even if further away much of the time in an emergency?"
I would assume that having a non-circular orbit, means the flight controllers can use the Moons gravity to maintain it's orbit without requiring "booster burns", when the orbital height gets a bit low.
This can save the need for fuel to be carried to HALO, in order to increase it's orbital height every once in a while (the ISS has to do this, as it's skimming Earths atmosphere which slows it down a little and it needs a "burn" to raise it's height - but getting fuel to the ISS is easy. Less so with the Moon).