What are the implications for me after a dream in which my father instructed me to fast for two days and take a sum of money? Should I fast and offer expiation on his behalf, and how much would that be?

A dream does not establish a ruling. If a deceased person has outstanding fasts, it is recommended for their guardian to fast on their behalf, as favored by Al-Nawawi and Ibn Qudamah, who cited the hadith: "Whoever dies with outstanding fasts, their guardian should fast on their behalf." Many scholars, however, held the view that no one should fast on their behalf, but rather food should be given as expiation. However, Al-Nawawi weakened these narrations. Based on this, it is permissible to fast or feed the poor on behalf of the deceased, and the reward for these actions will reach them.