Post-humans and aliens in the same setting.
I've long brainstormed a project for a Space Opera setting featuring various races, with a sort of 'fantasy in space' theme while not actually involving magic or the like, but instead making it thematically fantastical. However, as I sit down and consider how to populate this setting, I run against three roads: humans and aliens, all humans/post-humans, or humans, post-humans, and aliens.
In actuality I intend to feature aliens in the setting no matter what, the question is how prevalent they'll be in the current age of the setting, whether they'll exist purely as a sort mystery with alien precursor ruins scattered across the galaxy, or if there are actually still a few alien civilizations still kicking about the milky-way. Depending on which I choose, I have to then consider what role post-humans will take in my story.
I also plan on having them in the setting no matter what, but again, the question is how prevalent, and how I balance them against the existence of aliens in the same setting.
Going back to me wanting the universe to have a fantastical vibe, I want there to be a 'elvish' race. An ancient race of elegant beings with naturalistic philosophies and vibes, but I then run up against 'should I make them aliens, or make them post-humans who have diverged from normal humanity starkly enough?'
I'm curious about what anyone who has written a setting where both aliens and radically evolved humans has done, how they balance them against each other and what made them decide to make one of them one or the other.