The Goblin lair is very disorganized compared to the village of Darkstone and his people. Crude huts are everywhere, pigs and chickens run around, and giant spiders have their run of the place. The smell hits the party before they ever reach the lair and those who have a sensitive stomach it is quite a chore to carry on. Most of the goblins have only crude spears, though the goblins have clearly looted pieces of human armor and metal weapons.
If the party attacks, the goblins only fight in mobs and if they are whittled down to a few goblins, those goblins will try to run away. The number of goblins are up the GM. Really it depends on how many your party can handle.
There are also the giant spiders. These are standard monster manual giant spiders. The number is also up to the GM, but there should be quite a few.
Treasure is also up to the GM. These goblins have been raiding not only Darkston'e village, but surface villages as well, so they could have some good treasure.