What is meant by setting the "wheel" of Dharma in motion? Namo Buddhaya.

At many places in the texts it is said that the Buddha had set the wheel of dhamma in motion and that it can not be rolled back by anyone.
This sutta is devoted to the understanding of wheel of dhamma.

My questions are based on the above sutta(I am looking for the answer to the first question mainly but you can answer the rest if you want.) :


What is meant by setting the "wheel" of Dharma in motion? Why is it called a wheel?
In the sutta mentioned above following is said :



  But when my knowledge and vision of these Four Noble Truths as they
  really are in their three phases and twelve aspects was thoroughly
  purified in this way, then I claimed to have awakened


What are the three phases and twelve aspects of Dhamma?


In the same sutta mentioned above, Buddha says :



  “‘This noble truth of the origin of suffering is to be abandoned’:
  thus, bhikkhus, in regard to things unheard before, there arose in me
  vision, knowledge, wisdom, true knowledge, and light.


Why the noble Truth of the origin of suffering is to be abandoned ?
(I think craving needs to be abandoned and not the Truth)
You can read about the Dharma Wheel or Dharmachakra in the article "The Dharma Wheel (Dharmachakra) Symbol in Buddhism" by Barbara O'Brien.

In this article, it is stated that the Dharma Wheel is a chariot wheel and it is most commonly depicted as having eight spokes, representing the Noble Eightfold Path.

What happens when a chariot wheel is turned?

The chariot moves of course.

In this case, I suggest that it symbolizes that the chariot of humanity starts moving towards the end of suffering, towards Nibbana.