Is learning to play the Harp compulsory in heaven or will it be an automatic ability given you?

Exactly. Current "Christian" concepts of heaven and hell are tragically flawed. A good near-death experience will give you a much better picture of what it's like. (I recommend Betty Eadie's "Saved by the Light".) There's a lot more stuff going on there; the universe is expanding, new galaxies, solar systems and planets are coming on line all the time. We are God's children, and He invites us to take part in this expansion. It's a "family business" as it were.