It occurred to me to to wonder while thinking about NPCs whether characters with the Gift would have to buy Virtues in order to learn unholy Methods and Powers, or if they could learn them freely like other Supernatural Virtues?
waves at Aurelius
Serf's Parma, but I would imagine that you could learn them like other Supernatural Abilities. However, it quickly gets very difficult if you have other Supernatural Abilities already (unless you're a member of an Infernal Tradition and learning a Favored Ability).
I'm less certain. As I understand it, The Gift allows a character to learn supernatural abilities that are aligned with the Magic realm. This would exclude foreign Methods & Powers.
Of course, RoP: TI stresses the insidious nature of the Infernal and how easy it is to attain Infernal powers so a SG might be justified in allowing anyone who wants to learn Infernal powers to do so.
Yes, characters with The Gift can learn unholy Methods and Powers freely like other Supernatural Virtues. In fact, characters without The Gift can learn unholy Methods and Powers like other Supernatural Virtues. There's a section about learning them in the book. Serf's Parma, but IIRC, you just need to have been exposed to the Infernal somehow. It's ridiculously easy by design.