If there’s only one human player left in a game does that give immediate victory to that person regardless of how strong the AI opponents are? Or does the human still have to capture the required number of stars?

Sometimes if you make enough progress in the game, then hit shortcut key “L” to see the Leaderboard, and there you can find the button “Accept Victory”.

I’ve always had to get to more stars than any of the other empires, excepting the players who have afk’d.

pretty sure it mostly goes by stars and active player count. You can win if you get the required star amount, if you are the last active player alive with the most stars, or if people agree to concede to let whoever has the most stars win. Idk about the algorithm, I thought it was mostly off of star count, but I could be wrong.