Not to be picky or THAT guy, but actually your #5 wouldn't have made the list. Granted slavery in the Old Testament wasn't like it is today. Or at least not 100% of the time.

From the way I understand it, and from my brief reading of wikipedia to either support or debunk what I thought I knew, there were three ways you came to own slaves, or made use of your slaves: through conquest, to pay a debt, or for sexual purposes.

Slaves through conquest were the natives of conquered lands, who were forced to do work for Israel. And apparently was fully condoned in the Holiness Code from Leviticus (long as hell, but that's where it says the code is stated). Nations need workers, so God used the gentiles to fill that need. Gotta build a strong nation for God's chosen people.

Slaves of debt were basically just servants, or hired hands. There was one bible figure, whose name is escaping me, that agreed to work for a guy for seven years in order to marry one of the guy's daughters (the pretty one). After the seven years the guy was like "yeah, sure, you can have my daughter. ...buuuuut you never specified which one, so here's Slagathor. Good doing business with you." The guy, David I want to say, was pissed, but agreed to work for another seven years in order to marry the girl he wanted. Slavery of debt was perfectly fine, and I figure is even used in today's systems. Imagine community service if you will.

The final kind of slave was of the sexual variety. To my understanding they all weren't just basically hookers that you put a ring on. The purpose of these slaves, if I were to guess, were to grow the population/army size of Israel. And what do you need for that? Women. IIRC this usually went hand in hand with slave of conquest. "Okay, we just killed all your men and burned your city/cities to the ground, as per Yahwah's request. Now you're coming home with us and becoming out baby making machines. Good doing business with you."