From a biblical perspective, there is on problem with polygamy at all. We know this for many reasons. First, God himself gave David multiple wives, so it can't be wrong. And throughout the OT men who were under the direction of God had many wives and God never said a word against it (except once when warning that kings should not multiply too many wives). So that question is settled.
Now on to your points:
1. If polygamy is wrong, why did God allowed it and why do Muslims and some cultures still practice it?
It's not wrong according to the Bible. But even if it were, it would have nothing to do with the Muslim or Mormon practice of it because there is no reason to think that everything taught in Islam or Mormonism is true or good.
2. If polygamy is allowed by God and Muslims and some other culture, why not polyandry?
Because the religions were made up by men who were very sexist.
3. Do polygamy and polyandry have advantages over single marriage?
In some cases yes. For example, if there is an imbalance between the number of men and women. Too many women? Polygamy. Too many men? Polyandry. It's not a matter of morals at all.
4. Is polygamy and polyandry immoral?
Polygamy is obviously not immoral from a biblical perspective. But the Bible is silent about polyandry.
5. What is the difference between polygamy and polyandry compare to multiple divorces and remarriages, mistresses, concubines, multiple sex partners, adulteries, prostituition, wife/husband-swapping, one-night stand?
There are many differences. Marriage involves promises, so if you break promises with mistresses or adulteries, then that is immoral. But if your wife agrees and you are not deceiving the mistress then it is not immoral.
Things like prostitution and one-night stands are not moral issues so much as foolishness and risky because of health, pregnancy, and so forth. And they are usually foolish from a psychological/spiritual point of view too.
Spouse swapping is also probably foolish, but it's the decision of those who want to do it.
6. Why did modern and Western societies reject polygamy and embrace single marriage?
Because that's what they were taught be the Church.
7. Is single marriage entirely good?
Not necessarily. It can be horrible if you are wed to a horrible person.
8. Is multiple marriages good?
Depends upon what you mean. And the situation. You can't make general statements like saying it's always "good" or "bad." That thinking is too simplistic.
9. What do you all think about same-sex marriage?
Any couple who desires to be married should be allowed to do so.
Interesting questions. Thanks,
PS: It would be good if you quit making your stupid cracks about Rose. It's not very nice.