He then has to figure out each and every possible action he might take, and study all of their logical implications

Not all of their logical implications - the idea is to make use of tree pruning.

To do so he has to figure out the probability of each world state.

...except the ones you have dispensed with via tree pruning.

This further requires him to come up with a prior probability for each case and study all available data.

Not really - people typically work with whatever data they already have available in their existing world model.

As Kaj said, your brain is wired up to do a lot of this sort of thing unconsciously - and you should make use of the existing circuitry where you can.