The Nikah of Muhammad and Khadija

This question was bumped up in Quranology Discussions  today:

What is nikah? Must it be held in certain ritual ceremony? The nikah of Muhammad and Khadija was held in the pre-quranic era. How was it held?

If you ask me, I find these questions to be moot. If you revere Islamic History, fine but speculating details beyond what is already there is a little pointless I think. Focus on the task at hand: serving God.