Dear Brother Mubashir
As regards to your question of the crescent moon symbol over the mosques. It may be that it is linked directly to the Byzantine empire. At a certain point, it was the worlds most powerful empire. It was conquered by the Turks in 14th century. It is quite possible that the Turks appropriated the cultural symbols of the defeated Byzantines. Turkey became a Muslim empire and the rest of the Muslim world copied their symbols? This is possibly the reason that, to this day, the Turkish flag has a moon star symbol which is quite similar to the Byzantine flag.
Here's a link that may shed light on this matter.