If you haven't figured out the answer to your own question, maybe you need to not write the book just yet. It also seems to me that you are looking for an answer to a question that might not need to be asked.
The Gospel is not that complex.
Oh, no, it is a very good question and I think it is a very good question to ask. If prayer, that has been answered by God, is a good work (not towards salvation, but to a crown). Then you look at Eph. 2:10 which says that God has prepared good works from the foundation of the world that we should walk in them. Then the question goes to whether God planned these prayers.
Evidence that God planned prayers can be seen in Abimelech's dream in Genisis, where God tells Abimelech that Abramham would pray for him and that he and the women would be healed (God had shut the wombs). Also this is seen in Daniel when Michael (the Archangel) tells Daniel when he first set his mind on praying for the restoration of Jerusalem, the decree went forth.
Indications are that God is the one that initiates prayer (see Abraham again). So if God has planned prayer, prepared us for it, given us His word to pray, and ordained the answer. How should we then pray? What then is the power of prayer? Is it man, or God?