Rule reminder

Bisogna + infinitive = it is necessary (neutral register). Occorre + infinitive = it is necessary/required (formal, written). Serve/servono + noun = what is needed. Ci vuole + singular noun / Ci vogliono + plural noun = it takes / you need (quantity or effort). 'Occorre' is more formal than 'bisogna'; both are followed by an infinitive, never a noun.