We live in a beautiful, wonderful time for the planet where marriage equality and acceptance are more common than ever before. But that doesn't mean it's okay in the Tolkien universe. If we're sticking to canon, and I assume we are, homosexuality didn't exist. Technically, it's just never mentioned, so technically he never says there isn't homosexuality either, but I'd stay far away from it, personally. Not because of bigotry, but for the sake of the canon I hold so dear.
Think about 1940's Europe and America. Think about WWII propoganda. Think about the mindset of the world Tolkien was living in when he wrote these stories. Now think about gender roles in the books (and, for the sake of inclusion, the movies). Women and men held very different roles not so unlike the 40's culture Tolkien was a part of. Men were the soldiers. Men were the hunters. Men did the grunt work. Women did the cooking, the cleaning, the sewing, the child-rearing, etc. Both men and women did gender-neutral tasks like farming, leather-working, brewing, candle-making, etc. Then you've got women like Eowyn who stood out because they defied their roles. That doesn't mean Eowyn was the norm. What does that mean for us? I feel it can be a little less rigid than the homosexuality thing, just for the sake of play-ability. I'd say play what you want, but play it right. What I mean by that is this: if you're going to play a female soldier, RP out disdain from the vNPC population. If you're playing a male, RP out feeling annoyed that she's not doing a 'woman's work' if your PC wouldn't be used to that sort of thing. It doesn't mean you're actually a misogynist.
*ETA: I've been informed that while this is Tolkien canon, it's not SoI canon, wherein men and women are 100% equal. Which is fine, but I'm leaving it up anyway.
Names are so so SO important in the Tolkienverse. Names have meaning and power. Especially for higher races like Dunedain and elves and such, though that's not terribly applicable for us just yet. It's also traditional that sons are named after fathers after grandfathers, etc. That's why you end up with so many Stewards of the same name in Gondor's history. Even daughters tend to follow a family name 'trend.' Think about Theoden, Eowyn, and Eomer.
All of Tolkien's languages were based around real languages. Since we're in the north, our language (and Westron) developed out of his fictional language called Adûnaic, the language of the Numenoreans. The languages we use IG (as humans, not Orcs, I'm a little rusty on my Orc lore) are rooted in Old English and Nordic/Germanic tongues, and would probably sound a little rough. If you want an example of something that would probably sound similar to what we speak in game, click this link: https://www.youtube.com/watch?v=_K13GJkGvDw
If you aren't fluent in dead languages, this link can help you search words and tenses of words in Old English. It's where I create all my names. http://www.oldenglishtranslator.co.uk/
More modern names like Chad, Michael, Zachary, etc. make me cringe a little. But that's your prerogative. It's not canon, but it's you're prerogative.
Remember, Tolkien was a devout Catholic, so that means casual and premarital sex was a pretty big no-no. That's echoed in the Middle Earth realm. Sex is viewed in much the same way it is in the Christian Bible: not until marriage, but after that? Have at it, you crazy kids.
Elves choose one partner for life. Sex itself was literally the marriage "ceremony." There is no divorce, only death (or heading west). Something similar could be said for humanity, though it's a little less rigid. Casual sex probably happened. Divorce probably happened. Those who engaged in those sorts of things, however, were likely on par with criminals, if they were found out. There's an essay about this I read that talks about it, and you can read all 13 pages here if you want (it's really interesting, but I realize it's a niche sort of thing and I'm a mega-nerd): http://www.ansereg.com/WarmBedsareGood.pdf
Or, if you aren't so inclined, here are a couple important quotes from it:
Via its one acceptable road, marriage, sexual fulfillment is part of Happily Ever After for Tolkien.
Tl;dr: sex is for marriage, and is between a man and a woman in the Tolkienverse. Divorce is not common, and modern sexual stipulations are not applicable to canon.A final important aspect of sex and relationships in Middle-Earth is that Tolkien himself did not consider them in a modern context, but as part of his invented history. He deliberately did not place modern sexual dynamics or mores into Middle-Earth.
If you've read the books, think of the way they're written. If you've watched the movies, think of the way the characters speak. If you've seen anything to do with medieval Europe at all, think of the way those characters speak and you're on the right track. Modern swearing, slang, and phrases aren't really a thing in the Tolkienverse. Recall what your mother told you: think before you speak.
If anyone has anything to add or any corrections to make, please do. I'm tired and probably missed something, but this is what came to mind immediately. Here's what it comes down to for me: play whatever you want, however you want. If you're going to be a lesbian from Dale who swears like a sailor and can beat up a dude with her pinky, by all means, do it, if it's what you want. But don't pretend it's canon, and don't expect others who try to adhere to canon to treat your PC like it's totally normal.
-I've read The Silmarillion, The Hobbit, & The Trilogy, & have written multiple papers on this mess as well as had Tolkien-centric classes in college.