I do not think restitution requires buying all the media you copied. Besides, for most people who illegally copy music, games, and movies for their personal use, it would not be feasible because they don’t have that much spending money.
A more realistic (and lenient) view of restitution in this matter is to estimate how much you have actually harmed the media publishers. Question: If you had not illegally copied the stuff, how much would you have actually bought? That is how much they could have lost. The rationale for this “lenient” approach is that there is no direct loss to the publisher when you copy media illegally; they did not have to produce or package or web-host the illegal copies. Their losses are indirect, meaning they simply did not make the money they could have made by your purchases. So how much do you think that is?
In any case, I would follow the priest’s instructions regarding penance and restitution.
You have a lot of good questions. You should consider RCIA.