Even though I totally agree with Koog's response. For the sake of discussion I will try to answer your questions in order.
Yes
No, they can take multiple spouses if that is what everyone in that relationship dynamic wants but the government is not obliged to proved benefits for them beyond those that they would qualify for on their own.
No, animals aren't recognized as people so now legal marriage and no benefits. How ever if the guy wants to believe and live as if he and the goat are married. That is his prerogative
Yes
Yes
No because that right could harm another person
This is a one time shot just to give you a better understanding of how I perceive the Libertarian thinking. I'm not going to respond to other scenarios. Hope this helps