Is it possible to say how many moles are likely to be in an area?
1, they are solitary and very territorial, they only leave their area to mate. They do tunnel a lot each day though so 1 mole can do a lot of damage.
Do not use “humane” traps. Moles eat about 1/3rd of their body weight in worms every day, and dehydrate quickly. So unless you sit there watching the trap constantly then by the time you get to it you’ve got either a hungry, stressed and dehydrated mole, or a dead one, neither outcome is humane.
Do not release moles off your property. For one thing it’s illegal because they’re a pest, secondly you’ve just released a hungry, stressed, dehydrated mole into an others territory. They will fight, and your mole will lose, so it’s dead anyway (again, not humane). Even if there isn’t another mole, they store worms in a worm larder, so it’ll probably starve/dehydrate before it finds enough food anyway.
TLDR : Just kill it, there is no “humane” option.