What should one who fears a people do: Is it sufficient to merely supplicate, or should one strive beyond that with other means, taking into consideration that he meets them periodically? And is it permissible to offer greetings of peace to someone one dislikes for the sake of Allah, in order to guard against his evil? And how should one interact with him?

Supplication does not negate taking necessary measures. It is prescribed for a person to supplicate to Allah to protect him from the evil of those he fears, while simultaneously taking preventive measures. Greeting someone you dislike and fear their harm is not forbidden; rather, it might be a means of protecting you from their evil. Indeed, kindness can turn an enemy into a friend, as Allah Almighty says: "Repel [evil] with that which is best, and behold, he between whom and you was enmity will become as though he was a devoted friend." The Prophet (peace be upon him) would show a cheerful face to the man about whom he said, "What a bad brother of his tribe," to avert his evil. Al-Bukhari titled one of the narrations of this hadith: "Chapter on Conciliation with People."