Per the GOAP paper [0], yes. You can weight different actions. The example used is: Order pizza (to satisfy hunger) cost of 2, make a pie (to satisfy hunger) cost of 8. If the actor only satisfies the preconditions for one, that's what they do. But if they satisfy the preconditions for both, they take the cheaper one.

[0] http://alumni.media.mit.edu/~jorkin/goap.html

Yes, all actions have a cost associated with it.

You can use it in different ways: like you describe: have some agents prefer certain actions, different from the preferences of other agents.

The way I use it is to adapt to the environment. For instance, I make walking over to let's say an apple, less costly if the closest apple is near.