There isn't much to disagree with in your post. But I do want to correct something... When St Paul spoke to the men of Athens, he did mix something with the pure Gospel. He used an example from their own pagan writings to help in his explanation (Acts 17:28). It doesn't invalidate his witness. It was simply a tool to help their understanding.
This short video ‘about using the Koran for witnessing’ to Muslims is worth the listen. From Alpha and Omega Apologetics Ministries , and expresses my own concerns about using the Koran as a witness tool...especially regarding the Christ of Christianity on the same level as the Christ of the Koran.
I’d appreciate any comments as I do think in Witnessing to Muslims it’s important to get it right...
http://www.aomin.org/aoblog/index.php?itemid=4477