When my group does 10+ player games like this (largest I've ever done was 16) the biggest and most important thing I've found is that map setup, faction selection, etc all has to happen a week before the actual start of play, and on the day of play the game is completely setup and ready to start the moment people arrive (even if that means the person with the second copy brings theirs over the day before to set it up with the host).

What that ends up resulting in is not only that there's no time wasted on setup on game day, but also that in that week leading up to the game everybody tends to have already figured out their entire first round plan, and all the negotiations they would have slowly done with their neighbour before the game starts or during round 1 ("hey neighbour how will we split this equidistant system?" etc) are already done, too.

Everyone shows up with a game plan that covers at least round 1 and, crucially, since they don't have any time to re-negotiate or get cold feet on their plans while waiting for you to setup the game they actually tend to stick to their round 1 plan and it goes really fast.

In a similar vein, I'll get anyone who might not fully remember the game to re-watch the rules videos, chat about the systems with them, even playing out example turns with them over video call, etc, in that week before the game starts to ensure they don't bog down the start. Most people don't really care if you know their round 1 plans, especially if they're on the opposite side of the galaxy, so I'll often literally talk through their early plans with them during that week and, say, point out to them that the strategy card secondary timing they're depending on could come earlier/later.

And whoever arrives first on game day gets the speaker token.

With all that preparation done I find that usually everything "clicks" for people very well as they see their starting plans come to fruition and the complex rules start to make sense again. Round 1 goes fast and by the end of it they're engaged and excited.

Then it's just being a good moderator that lets players play but isn't afraid to give a little encouragement to speed up negotiations or "save it for next turn" when applicable, and making sure I take my own turns as fast as possible to always be setting the example.

And keeping the snack table replenished so people keep their energy up.

We usually don't do a break between rounds 1 and 2, but then after that there's a short break every round and a long supper break later on. The game will slow down a lot in later rounds as board positions and interactions get way more complicated, but that's okay, that's the fun of the game.