These are just my opinions but I'm personally not a fan of the antagonist becoming transgender "mostly just so they could become the leader of their society"... I'm sure there's more details to it all since we're only getting snippets but it doesn't feel like a good choice to have a character be "fake trans" to be evil, like a "gotcha" moment. Maybe consider other factors that could give them the same effect? Or they could just be trans because they're trans, not for gaining power in your verse. Even framing it a different way can help, like having the character transition when they're younger and realizing later on that they have more power as their true self. Just not being trans because of a power advantage in particular.
For Laurnyas, so long as it's not a sudden thing to slap on at the end, I think you're fine. Little things like seeming uninterested in women or an "I don't want to" moment go a long way. Doesn't need to be a big production.
And with mentioning things "just once", how come? I feel it wouldn't distract any from the story, being LGBT does affect people a lot. If anything seeing it mentioned more than once is validating! Otherwise it can be seen as tokenism.
You're free to ask more stuff! But having a little more in-depth info might help with specifics. I'd like to hear about your universe and its standards, like how it fares compared to ours. It can help a lot with how to handle different issues, characters, dynamics, stuff like that.