I'd suggest "smart" tutorials and alerts, into the game. Pop-up that appear for each "new" event that happens, and possibly other alerts, or issues in your empire status. Examples for that can be seen in rimworld or stellaris. For people that don't know this concept, basically... when the player encounters something new and / or an event happens, an icon appears the side of the map. When you click on the icon an explanation is displayed as a pop-up, what the issue is, and how to basically deal with it.
For example, when entering a system with a raid engine, it explains that it'll send raids every 4 minutes if the adjacent planet is neutered, and concept of "deep strikes", possibily with transports. If a science station appears, it tells the player that you need to conquer the planet to gain the extra ship to build.
This kind of pop-up can also be tied to empire status, like "you're low on mineral, here's how to increase production", or alerts, like "hey, you forgot to rebuild a resource collector, here is how to automate rebuild".
I think that fits AI war better than "mission-based" tutorials.
