you are perhaps asking several questions under one title, but I assume the single essence of your question to be the attitude of Islam toward women. So here is a brief answer, far from being comprehensive.
Rules are assumed to be based on justice, and justice means "anything in its own right place", so if two entities are different in any aspect of their existence they should be treated differently. So, for example someone who knows a deed is wrong but commit, should be differently treated compared to someone who knows not. Similarly, man and woman are both humans, so should be treated equally when it comes to being human/non-human. But beside that, certainly man and woman are different in several bold aspects of life. The souls are equal, but the body and psychology are in many ways different between the two genders. So in Islam we do not believe the rules which govern the personal/social lives of the two genders should be equal, but justice is that each one is ruled by a set of rules suitable for themselves. In Islam, man and woman should be able to take their parts in community, but as human being, not making bold their genders, which has function only in the smallest community-subset, the family. Covering the hair and the protuberances in an adult female body, is to cover the gender-explicity of those humans who if otherwise they do not cover them, it will inject their gender-related factors into the community, where it is not a place for that sort of things. This is not required for men that much strictly (though it still has its rules, even the holy prophet PBUHH was afraid to pray Allah not wearing a hat or anything to cover his head, even though praying is usually considered personal with least social effects) because of the difference between men and women. For example, men are easily seduced by looking at female bodies, while the reverse is rarely true. Women being uncovered in the society, will in average weaken the relations between couples, and many other consequences counted by the scholars.
Polygamy is another thing, so much debated. Some believe it being allowed is only limited to special conditions. Some believe it being allowed and even encouraged but only in special conditions. Some believe it was limited to four wives at a time when Arabs used to assume no limit for it, so to bold its limitation rather than its anyway being allowed. But anyway, it has many limitations, and there are warnings against it even in Quran, such that it can be a situation for women to go astray and family members to hate each other that again weakens the families. I bring here three examples from Quran.
Ibrahim's wife's envy and zealousy against Hajar, who was once her servant but suggested her to her own husband Ibrahim PBUH to marry with, so to be able to have a child. This jealousy yields into Hajar and Ismaeil PBUH being rejected to Mecca, to live there in a desert with no apparent water to drink, or food to eat.
Jacob's wives and the enmity between his sons against Joseph PBUH, which was rooted in envy between the sons' two mothers toward Joseph and Benjamin, PBUT.
إِذْ قَالُوا لَيُوسُفُ وَ أَخُوهُ أَحَبُّ إِلَيٰ أَبِينَا مِنَّا وَ
نَحْنُ عُصْبَةٌ إِنَّ أَبَانَا لَفِي ضَلَالٍ مُبِينٍ
They said: 'Truly Joseph and his brother are loved more by our father
than we: But we are a goodly body! really our father is obviously
wandering (in his mind)!
- Harun's calling Moses as "يَا ابْنَ أُمَّ" which means "my mother's son", which according to a Shia Hadeeth was to remind Moses PBUH that they are both from one single mother, so that they should be kinder to each other compared to those from different mothers.
Do such examples prove Polygamy wrong, or exceptional, or unwise? certainly not! But it is not so easy as well. This is a place of several difficulties for all the family members, be it the man, the women, or even the kids to be born in the family, and grow. If a society accepts it in average, the situation would be easier for all, though still having its inherit difficulties. Last but not least, mention that Islam allows such relations in a structure called Marriage, which has its own rules, and is way different than making relationships with no governing rule at all. So a husband has his own rights and his own duties, with his duties becoming heavier when having more than one wife, while each wife has also her own rights and her own duties, which her duties might become lighter when she is not the only wife. Even you may not know, but there is another kind of marriage in Islam, called متعه which is a temporal marriage (historically almost all sects in Islam accepts this sort of marriage was once allowed in Islam, but as far as I know at the present only Shia Islam approves it now, as the second Caliphate made it Haram after the holy prophet PBUHH declare it allowed). The rules governing families in Islam are so many, and sometimes diverse for different situations, which shows how important the concept of a family is in the view of Islam.
