Follow up question also, did sex slaves flourish at the time amongst the first muslims? What rights did the sex slaves had? Did they has the responsibility to work as other slave, or did their job was merely to dress up and, erm, have sex?
In terms of "sex slaves" this really wasn't a thing. Unmarried female slaves in general had sexual relations with their owners but they weren't typically designated as "sex"' slaves. In terms of rights, they had the same right as any other slaves, with one extra. Enslavement occurred through two ways: being captured in war, or being born into slavery. They had the right to earn what was called a "mukataba" which was a contract delineating how long they would work in order to be freed. The slave was due shelter, food, clothing, and medical attention from his/her master.. The standard of the food and clothing was required to be equivalent to the standard in the locality. The extra right given to an unmarried female slave is that if she were to become pregnant, she could no longer be sold and would be automatically freed at her owner's death.
Source and further reading: The Social Structure of Islam by Reuben Levy.
Hmm, these two questions have absolutely nothing to do with each other so I'll answer them separately.
At once, 9 wives. I think over his lifetime though, it comes to 12.