I'm not a scholar, so all of this should be taken as my best effort based on my own understanding.
Re: polygamy.
The actual guidance is that men should be faithful to their wives, and there is wider guidance that, unless a society's laws are actively un-Islamic, Muslims should follow the legal system of the country in which they live. So, if someone lives in a country where polygamy isn't acceptable, they shouldn't go looking to have multiple spouses.
A man should only ever be considering having more than one wife if a) he lives in a society in which it is legal and acceptable; b) he can treat his wives equally well. Otherwise, nope, no second wives (or however many) allowed.
There are academic discussions that can be had about polygamy in different cultures and different times, but those probably aren't that relevant here.
Re: The wives of The Prophet, Peace Be Upon Him, having several husbands at the same time, no they didn't, to my knowledge. I don't know if other Prophets or Messengers may have or not, Allah Knows Best. When thinking about that time, it's important to consider that the wider society pre-Islam was pretty misogynistic - some of the teachings and examples from that time, from the early days of Islam, were pretty shocking in terms of promoting and protecting women's rights. Rights to divorce, to inherit, to testify in court...
When we look at aspects of that time from a modern and Western perspective, there are things that we would say "Well, that's not ok in our society today!", but the guidance in Islam wasn't and isn't just for our current society. It's important to consider the underlying principles and themes, the contexts, and the historical purposes of some of the things.
For example, child marriage. Definitely, absolutely not acceptable in our UK society. Historically, it's something that's happened a lot. And even today there are cultures in which it happens, places in which the age of consent for sexual activity is much lower than here. I disagree with those cultures' views. I hope most people posting here also don't agree with child marriage. Historically, it was a common practice and it was common for children to be subjected to horrific abuse as a result. It was a big step for men to be told that, if they were marrying an underage child, they shouldn't consider consummating the marriage until she was 'of age', and they should treat her with love and respect.
'Don't sexually assault children' is an extremely low bar for men, but so many fall short, even today.
Re: Rewards in Heaven, there's no reason to believe that only men get to have a nice time or get companionship or to be with their loved ones. The masculine plurals for people are used, but in Arabic the masculine plurals are used for all-male or mixed-sex groups - only an all-female group would be referred to using the feminine plurals.